• 

ff 


MEMCAL    SCHOOL 


SMITHSONIAN   MISCELLANEOUS   COLLECTIONS 

-  '075  — 

THE  CONSTANTS  OF  NATURE 

PART  V 
A   RECALCULATION 


OF 


THE    ATOMIC    WEIGHTS 


BY 


FRANK  WIGGLESWORTH  CLARKE 

Chief  Chemist  of  the  U.  S.  Geological  Survey 


NEW  EDITION,  REVISED  AND  ENLARGED 


CITY   OF   WASHINGTON 

PUBLISHED  BY  THE  SMITHSONIAN  INSTITUTION 
1897 


JUDD  &  DETWEILER,  PRINTERS 
WASHINGTON,  D.  C. 


ADVERTISEMENT. 


The  present  publication  is  one  of  a  series  devoted  to  the  discussion 
and  more  precise  determination  of  various  u  Constants  of  Nature;  "  and 
forms  the  Fifth  contribution  to  that  subject  published  by  this  Institution. 

The  First  number  of  the  series,  embracing  tables  of  u  Specific  Gravi- 
ties "  and  of  Melting  and  Boiling  Points  of  Bodies,  prepared  by  the  same 
author,  Prof.  F.  W.  Clarke,  was  published  in  1873.  The  Fourth  part  of 
the  series,  comprising  a  complete  digest  of  the  various  "Atomic  Weight " 
determinations  of  the  chemical  elements  published  since  1814,  com- 
mencing with  the  well-known  "  Table  of  Equivalents  "  by  Wollaston 
(given  in  the  Philosophical  Transactions  for  that  year),  compiled  by 
Mr.  George  F.  Becker,  was  published  by  the  Institution  in  1880.  The 
present  work  comprises  a  very  full  discussion  and  recalculation  of  the 
"Atomic  Weights"  from  all  the  existing  data,  and  the  assignment  of 
the  most  probable  value  to  each  of  the  elements. 

The  first  edition  of  this  work  was  published  in  1882,  and  this  new 
edition,  revised  and  enlarged  by  Professor  Clarke,  contains  new  informa- 
tion accumulated  during  the  past  fifteen  years. 

S.  P.  LANGLEY, 
Secretary  of  the  Smithsonian  Institution. 

WASHINGTON,  January,  1897. 


13393 


TABLE  OF  CONTENTS 


PAGE. 

Introduction , i 

Formulae  for  the  Calculation  of  Probable  Error 7 

1 .  Oxygen 8 

2.  Silver,  Potassium,  Sodium,  Chlorine,  Bromine,  and  Iodine 34 

3.  Nitrogen 58 

4.  Carbon 72 

5.  Sulphur 80 

6.  Lithium 84 

7.  Rubidium v 87 

8.  Caesium 89 

9.  Copper 91 

10.  Gold 101 

1 1 .  Calcium no 

12.  Strontium 1 13 

13.  Barium 1 18 

14.  Lead 127 

15.  Glucinum 132 

16.  Magnesium 135 

1 7.  Zinc 146 

18.  Cadmium 156 

19.  Mercury ., 166 

20.  Boron 171 

21.  Aluminum    J76 

22.  Gallium 181 

23.  Indium 182 

24.  Thallium 184 

25.  Silicon 188 

26.  Titanium 190 

27.  Germanium 195 

28.  Zirconium , 196 

29.  Tin 199 

30.  Thorium 204 

31.  Phosphorus 209 

32.  Vanadium 211 

33.  Arsenic 213 

34.  Antimony 4 216 

35.  Bismuth 229 

36.  Columbium 234 

37.  Tantalum 236 

38.  Chromium 238 

39.  Molybdenum 250 

40.  Tungsten 255 

41 .  Uranium 263 

42.  Selenium 268 

43.  Tellurium 271 

44.  Fluorine ...... 277 

(v) 


VI  TABLE    OF    CONTENTS. 

PAGE. 

45.  Manganese 282 

46.  Iron .    287 

47.  Nickel  and  Cobalt 291 

48.  Ruthenium 311 

49.  Rhodium ,  313 

50.  Palladium 315 

51.  Osmium , 322 

52.  Iridium 325 

53.  Platinum 327 

54.  Cerium 335 

55.  Lanthanum.. 344 

56.  The  Didymiums 351 

57.  Scandium 354 

58.  Yttrium 355 

59.  Samarium,  Gadolinium,  "Erbium,  and  Ytterbium .  359 

60.  Terbium,  Thulium,  Holmium,  Dysprosium,  etc , .  362 

61.  Argon  and  Helium 363 

Table  of  Atomic  Weights 364 

Index  . . 367 


A  RECALCULATION"  OF  THE  ATOMIC  WEIGHTS. 


BY  FRANK  WIGGLESWORTH  CLARKE. 


INTRODUCTION. 

In  the  autumn  of  1877  the  writer  began  collecting  data  relative  to 
determinations  of  atomic  weight,  with  the  purpose  of  preparing  a  com- 
plete resume  of  the  entire  subject,  and  of  recalculating  all  the  estima- 
tions. The  work  was  fairly  under  way,  the  material  was  collected  and 
partly  discussed,  when  I  received  from  the  Smithsonian  Institution  a 
manuscript  by  Professor  George  F.  Becker,  entitled  "  Atomic  Weight 
Determinations:  a  Digest  of  the  Investigations  Published  since  1814." 
This  manuscript,  which  has  since  been  issued  as  Part  IV  of  the  "  Con- 
stants of  Nature,"  covered  much  of  the  ground  contemplated  in  my  own 
undertaking.  It  brought  together  all  the  evidence,  presenting  it  clearly 
and  thoroughly  in  compact  form  ;  in  short,  that  portion  of  the  task  could 
not  well  be  improved  upon.  Accordingly,  I  decided  to  limit  my  own 
labors  to  a  critical  recalculation  of  the  data ;  to  combine  all  the  figures 
upon  a  common  mathematical  basis,  and  to  omit  everything  which  could 
as  well  be  found  in  Professor  Becker's  "  Digest." 

In  due  time  my  work  was  completed,  and  early  in  1882  it  was  pub- 
lished. About  a  year  later  Meyer  and  Seubert's  recalculation  appeared, 
to  be  followed  later  still  by  the  less  elaborate  discussions  of  Sebelien  and 
of  Ostwald.  All  of  these  works  differed  from  one  another  in  various 
essential  particulars,  presenting  the  subject  from  different  points  of  view, 
and  with  different  methods  of  calculation.  Each  one,  therefore,  has  its 
own  special  points  of  merit,  and,  in  a  sense,  reinforces  the  others.  At 
the  same  time,  the  scientific  activity  which  they  represent  shows  how 
widespread  was  the  interest  in  the  subject  of  atomic  weights,  and  how 
fundamentally  important  these  constants  undoubtedly  are. 

The  immediate  effect  of  all  these  publications  was  to  render  manifest 
the  imperfections  of  many  of  the  data,  and  to  point  out  most  emphatic- 
ally in  what  directions  new  work  needed  to  be  done.  Consequently,  there 
has  been  since  1884  an  extraordinary  activity  in  the  determination  of 
atomic  weights,  and  a  great  mass  of  new  material  has  accumulated.  The 
assimilation  of  this  material,  and  its  combination  with  the  old  data,  is 
the  object  of  the  present  volume. 

(1) 


2  THE   ATOMIC   WEIGHTS. 

At  the  very  beginning  of  my  work,  certain  fundamental  questions  con- 
fronted me.  Should  I  treat  the  investigations  of  different  individuals 
separately,  or  should  I  combine. similar  data  together  in  a  manner  irre- 
spective of  persons  ?  For  example,  ought  I,  in  estimating  the  atomic 
weight  of  silver,  to  take  Stas'  work  by  itself,  Marignac's  work  by  itself, 
and  so. on,  and  then  average  the  results  together;  or  should  I  rather 
combine  all  series  of  figures  relating  to  the  composition  of  potassium 
chlorate  into  one  mean  value,  and  all  the  data  concerning  the  composi- 
tion of  silver  chloride  into  another  mean,  and,  finally,  compute  from  such 
general  means  the  constant  sought  to  be  established  ?  The  latter  plan 
was  finally  adopted ;  in  fact,  it  was  rendered  necessary  by  the  method  of 
least  squares,  which,  in  a  special,  limited  form,  was  chosen  as  the  best 
method  of  dealing  with  the  problem. 

The  mode  of  discussion  and  combination  of  results  was  briefly  as 
follows.  The  formula  employed  are  given  in  another  chapter.  I  began 
with  the  ratio  between  oxygen  and  hydrogen ;  in  other  words,  with  the 
atomic  weight  of  oxygen  referred  to  hydrogen  as  unity.  Each  series  of 
experiments  was  taken  by  itself,  its  arithmetical  mean  was  found,  and 
the  probable  error  of  that  mean  was  computed.  Then  the  several  means 
were  combined  according  to  the  appropriate  formula,  each  receiving  a 
weight  dependent  upon  its  probable  error.  The  general  mean  thus  estab- 
lished was  taken  as  the  most  probable  value  for  the  atomic  weight  of 
oxygen,  and,  at  the  same  time,  its  probable  error  was  mathematically 
assigned. 

Next  in  order  came  a  group  of  elements  which  were  best  discussed 
together,  namely,  silver,  chlorine,  potassium,  sodium,  bromine,  and 
iodine.  For  these  elements  there  were  data  from  many  experimenters. 
All  similar  figures  were  first  reduced  to  common  standards,  and  then 
the  means  of  individual  series  were  combined  into  general  means.  Thus 
all  the  data  wrere  condensed  into  nineteen  ratios,  from  which  several 
independent  values  for  the  atomic  weight  of  each  element  could  be 
computed.  The  probable  errors  of  these  values,  however,  all  involved 
the  probable  error  of  the  atomic  weight  of  oxygen,  and  were,  therefore, 
higher  than  they  would  have  been  had  the  latter  element  not  entered 
into  consideration.  Here,  then,  we  have  suggested  a  chief  peculiarity 
of  this  whole  revision.  The  atomic  weight  of  each  element  involves 
the  probable  errors  of  all  the  other  elements  to  which  it  is  directly  or 
indirectly  referred.  Accordingly,  an  atomic  weight  determined  by  refer- 
ence to  elements  whose  atomic  weights  have  been  defectively  ascertained 
will  receive  a  high  probable  error,  and  its  weight,  when  combined  with 
other  values,  will  be  relatively  low.  For  example,  an  atomic  weight 
ascertained  by  direct  comparison  with  hydrogen  will,  other  things  being 
equal,  have  a  lower  probable  error  than  one  which  is  referred  to  hydro- 
gen through  the  intervention  of  oxygen  ;  and  a  metal  whose  equivalent 
involves  only  the  probable  error  of  oxygen  should  be  more  exactly 


INTRODUCTION.  3 

/ 

known  than  one  which  depends  upon  the  errors  of  silver  and  chlorine. 
These  points  will  appear  more  clearly  evident  in  the  subsequent  actual 
discussions. 

But  although  the  discussion  of  atomic  weights  is  ostensibly  mathe- 
matical, it  cannot  be  purely  so.  Chemical  considerations  are  necessarily 
involved  at  every  turn.  In  assigning  weights  to  mean  values  I  have 
been,  for  the  most  part,  rigidly  guided  by  mathematical  rules ;  but  in 
some  cases  I  have  been  compelled  to  reject  altogether  series  of  data 
which  were  mathematically  excellent,  but  chemically  worthless  because 
of  constant  errors.  In  certain  instances  there  were  grave  doubts  as  to 
whether  particular  figures  should  be  included  or  rejected  in  the  calcula- 
tion of  means,  there  having  been  legitimate  reasons  for  either  procedure. 
Probably  many  chemists  would  differ  with  me  upon  such  points  of  judg- 
ment. In  fact,  it  is  doubtful  whether  any  two  chemists,  working  inde- 
pendently, would  handle  all  the  data  in  precisely  the  same  way,  or 
combine  them  so  as  to  produce  exactly  the  same  final  results.  Neither 
would  any  two  mathematicians  follow  identical  rules  or  reach  identical 
conclusions.  In  calculating  the  atomic  weight  of  any  element  those 
values  are  assigned  to  other  elements  which  have  been  determined  in 
previous  chapters.  Hence  a  variation  in  the  order  of  discussion  might 
lead  to  slight  differences  in  the  final  results. 

As  a  matter  of  course  the  data  herein  combined  are  of  very  unequal 
value.  In  many  series  of  experiments  the  weighings  have  been  reduced 
to  a  vacuum  standard ;  but  in  most  cases  chemists  have  neglected  this 
correction  altogether.  In  a  majority  of  instances  the  errors  thus  intro- 
duced are  slight ;  nevertheless  they  exist,  and -interfere  more  or  less  with 
all  attempts  at  a  theoretical  consideration  of  the  results. 

Necessarily,  this  work  omits  many  details  relative  to  experimental 
methods,  and  particulars  as  to  the  arrangement  of  special  forms  of  appa- 
ratus. For  such  details  original  memoirs  must  be  consulted.  Their  in- 
clusion here  would  have  rendered  the  work  unwarrantably  bulky.  There 
is  such  a  thing  as  over-exhaustiveness  of  treatment,  which  is  equally 
objectionable  with  under-thoroughness. 

Of  course,  none  of  the  results  reached  in  this  revision  can  be  consid- 
ered as  final.  Every  one  of  them  is  liable  to  repeated  corrections.  To 
my  mind  the  real  value  of  the  work,  great  or  little,  lies  in  another  direc- 
tion. The  data  have  been  brought  together  and  reduced  to  common 
standards,  and  for  each  series  of  figures  the  probable  error  has  been  de- 
termined. Thus  far,  however  much  my  methods  of  combination  may 
be  criticised,  I  feel  that  my  labors  will  have  been  useful.  The  ground  is 
cleared,  in  a  measure,  for  future  experimenters;  it  is  possible  to  see  more 
distinctly  what  remains  to  be  done ;  some  clues  are  furnished  as  to  the 
relative  merits  of  different  series  of  results. 

On  the  mathematical  side  my  method  of  recalculation  has  obvious 
deficiencies.  It  is  special,  rather  than  general,  and  at  some  future  time, 
when  a  sufficiently  large  mass  of  evidence  has  accumulated,  it  must 


4  THE   ATOMIC   WEIGHTS. 

give  way  to  a  more  thorough  mode  of  treatment.  For  example,  the  ratio 
Ag2 :  BaBr2  has  been  used  for  computing  the  atomic  weight  of  barium, 
the  atomic  weights  of  silver  and  bromine  being  supposed  to  be  known. 
But  these  atomic  weights  are  subject  to  small  errors,  and  they  are  super- 
imposed upon  that  of  the  ratio  itself  in  the  process  of  calculation.  Ob- 
viously, the  ratio  should  contribute  to  our  knowledge  of  all  three  of  the 
atomic  weights  involved  in  it,  its  error  being  distributed  into  three  parts 
instead  of  appearing  in  one  only.  The  errors  may  be  in  part  compensa- 
tory ;  but  that  is  not  certainly  known. 

Suppose  now  that  for  every  element  we  had  a  goodly  number  of  atomic 
weight  ratios,  connecting  it  with  at  least  a  dozen  other  elements,  and  all 
measured  with  reasonable  accuracy.  These  hundreds  of  ratios  could 
then  be  treated  as  equations  of  observation,  reduced  to  linear  form,  and 
combined  by  the  general  method  of  least  squares  into  normal  equations. 
All  errors  would  thus  be  distributed,  never  becoming  cumulative ;  and 
the  normal  equations,  solved  once  for  all,  would  give  the  atomic  weights 
of  all  the  elements  simultaneously.  The  process  would  be  laborious 
but  the  result  would  be  the  closest  possible  approach  to  accuracy.  The 
data  as  yet  are  inadequate,  although  some  small  groups  of  ratios  may 
be  handled  in  that  way ;  but  in  time  the  method  is  sure  to  be  applied, 
and  indeed  to  be  the  only  general  method  applicable.  Even  if  every  ratio 
was  subject  to  some  small  constant  error,  this,  balanced  against  the 
similar  errors  of  other  ratios,  would  become  accidental  or  unsystematic 
with  reference  to  the  entire  mass  of  material,  and  would  practically 
vanish  from  the  final  means. 

Concerning  this  subject  of  constant  and  accidental  errors,  a  word  may 
be  said  here.  My  own  method  of  discussion  eliminates  the  latter,  which 
are  removable  by  ordinary  averaging ;  but  the  constant  errors,  vicious 
and  untractable,  remain,  at  least  partially.  Still,  where  many  ratios 
are  considered,  even  the  systematic  errors  may  in  part  compensate  each 
other,  and  do  less  harm  than  might  be  expected.  They  have,  moreover, 
a  peculiarity  which  deserves  some  attention. 

In  the  discussion  of  instrumental  observations,  the  systematic  errors 
are  commonly  constant,  both  as  to  direction  and  as  to  magnitude.  They 
are  therefore  independent  of  the  accidental  errors,  and  computation  of 
means  leaves  them  untouched.  But  in  the  measurement  of  chemical 
ratios  the  constant  errors  are  most  frequently  due  to  an  impurity  in  one 
of  the  materials  investigated.  If  different  samples  of  a  substance  are 
studied,  although  all  may  contain  the  same  impurity,  they  are  not  likely 
to  contain  it  in  the  same  amount ;  and  so  the  values  found  for  the  ratio 
will  vary.  In  other  words,  such  errors  may  be  constant  in  direction  but 
variable  in  magnitude.  That  variation  appears  in  the  probable  error 
computed  for  the  series  of  observations,  diminishes  its  weight  when  com- 
bined with  other  series,  and  so,  in  part,  corrects  itself.  It  is  not  removed 
from  the  result,  but  it  is  self-mitigated.  The  constant  errors  familiar  to 
the  physicist  and  astronomer  are  obviously  of  a  different  order. 


INTRODUCTION.  5 

That  all  methods  of  averaging  are  open  to  objections,  I  am  of  course 
perfectly  aware.  I  also  know  the  doubts  which  attach  to  all  questions 
of  probable  error,  and  to  all  combinations  of  data  which  depend  upon 
them.  I  have,  however,  preferred  to  face  these  objections  and  to  recog- 
nize these  doubts  rather  than  to  adopt  any  arbitrary  scheme  which  per- 
mits of  a  loose  selection  of  data.  After  all,  the  use  of  probable  error  as 
a  means  of  weighting  is  but  a  means  of  weighting,  and  perhaps  more 
justifiable  than  any  other  method  of  attaining  the  same  result.  When 
observations  are  weighted  empirically — that  is,  by  individual  judg- 
ment— far  greater  dangers  arise.  Almost  unconsciously,  the  work  of  a 
famous  man  is  given  greater  weight  than  that  of  some  obscure  chemist, 
although  the  latter  may  ultimately  prove  to  be  the  best.  But  the  prob- 
able error  of  a  series  of  measurements  is  not  affected  by  the  glamor  of 
great  names;  and  the  weight  which  it  assigns  to  the  observations  is  at 
least  as  safe  as  any  other.  In  the  long  run,  I  believe  it  assigns  weight 
more  accurately,  and  therefore  I  have  trusted  to  its  indications,  not  as 
if  it  were  a  mathematical  fetish,  but  regarding  it  as  a  safe  guide,  even 
though  sometimes  fallible. 

In  Meyer  and  Seubert's  recalculation,  weights  are  assigned  in  quite  a 
novel  manner.  In  each  series  of  experiments  the  maximum  and  mini- 
mum results  are  given,  but  instead  of  the  mean  there  is  a  value  deduced 
from  the  sum  of  the  weighings — that  is,  each  experiment  is  weighted 
proportionally  to  the  mass  of  the  material  handled  in  it.  For  this 
method  I  am  unable  to  find  any  complete  justification.  Of  course,  the 
errors  due  to  the  operations  of  weighing  become  proportionally  smaller 
as  the  quantity  of  material  increases,  but  these  errors,  with  modern 
apparatus,  are  relatively  unimportant.  The  real  errors  in  atomic  weight 
determinations  are  much  larger  than  these,  and  due  to  different  causes. 
Hence  an  experiment  upon  ten  grammes  of  material  may  be  a  little  better 
than  one  made  upon  five  grammes,  but  it  is  by  no  means  necessarily 
twice  as  good.  The  ordinary  mean  of  a  series  of  observations,  with  its 
measure  of  concordance,  the  probable  error,  is  a  better  value  than  one 
obtained  in  the  manner  just  described.  If  only  errors  of  weighing  were 
to  be  considered,  Meyer  and  Seubert's  summation  method  would  be 
valid,  but  in  the  presence  of  other  and  greater  errors  it  seems  to  have 
but  little  real  pertinency  to  the  problem  at  hand. 

In  addition  to  the  usual  periodicals,  the  following  works  have  been 
freely  used  by  me  in  the  preparation  of  this  volume: 

BERZELIUS,  J.  J.  Lehrbuch  der  Chemie.  5  Auflage.  Dritter  Band. 
SS.  1147-1231.  1845. 

VAN  GEUNS,  W.  A.  J.  Prceve  eener  Geschiedenis  van  de  ^Equivalent- 
getallen  der  Scheikundige  Grondstoffen  en  van  hare  Soortelijke 
Gewigten  in  Gasvorm,  voornamelijk  in  Betrekking  tot  de  vier 
Grondstoffen  der  Bewerktuigde  Natuur.  Amsterdam,  1853. 


O  THE   ATOMIC   WEIGHTS. 

MULDER,  E.  Historisch-Kritisch  Overzigt  van  de  Bepalingen  der  JEquiv- 
alent-Gewigten  van  13  Eenvoudige  Ligchamen.  Utrecht,  1853. 

MULDER,  L.  Historisch-Kritisch  Overzigt  van  de  Bepalingen  der  JLquiv- 
alent-Gewigten  van  24  Metalen.  Utrecht,  1853. 

OUDEMANS,  A.  C.,  Jr.  Historisch-Kritisch  Overzigt  van  de  Bepaling  der 
^Equivalent-Gewigten.  van  Twee  en  Twintig  Metalen.  Leiden, 
1853. 

STAS,  J.  S.  Untersuchungen  iiber  die  Gesetze  der  Chemischen  Propor- 
tionen  iiber  die  Atomgewichte  und  ihre  gegenseitigen  Verhalt- 
nisse.  Uebersetzt  von  Dr.  L.  Aronstein.  Leipzig,  1867. 

See  also  his  "  Oeuvres  Completes,"  3  vols.,  published  at  Bruxelles 
in  1894. 

MEYER,  L.,  and  SEUBERT,  K.  Die  Atomgewichte  der  Elemente,  aus  den 
Originalzahlen  neu  berechnet.  Leipzig,  1883. 

SEBELIEN,  J.    Beitrage  zur  Geschichte  der  Atomgewichte.    Braunschweigy 

1884. 

OSTWALD,  W.  Lehrbuch  der  allgemeinen  Chemie.  Zweite  Aufl.  I 
Band.  SS.  18-138.  Leipzig,  1891. 

The  four  Dutch  monographs  above  cited  are  especially  valuable. 
They  represent  a  revision  of  all  atomic  weight  data  down  to  1853,  as 
divided  between  four  writers. 

For  the  sake  of  completeness  the  peculiar  volume  by  Hinrichs  *  must 
also  be  cited,  although  the  methods  and  criticisms  embodied  in  it  have 
not  been  generally  endorsed.  Hinrichs'  point  of  view  is  so  radically 
different  from  mine  that  I  have  been  unable  to  make  use  of  his  discus- 
sions. His  objections  to  the  researches  of  Stas  seem  to  be  quite  un- 
founded ;  and  the  rejoinders  by  Spring  and  by  Van  der  Plaats  are  suffi- 
ciently thorough. 

*  The  True  Atomic  Weight  of  the  Chemical  Elements  and  the  Unity  of  Matter.  St.  I^ouis,  1894. 
Compare  Spring,  Chem.  Zeitung,  Feb.  22,  1893,  and  Van  der  Plaats,  Compt.  Rend.,  116,  1362.  See 
also  a  paper  by  Vogel,  with  adverse  criticisms  by  Spring  and  L,.  Henry,  in  Bull.  Acad.  Bruxelles, 
(3),  26,  469. 


INTRODUCTION. 


FORMULAE  FOR  THE  CALCULATION  OF  PROBABLE  ERROR. 

The  formula  for  the  probable  error  of  an  arithmetical  mean,  familiar 
to  all  physicists,  is  as  follows : 


Here  n  represents  the  number  of  observations  or  experiments  in  the 
series,  and  S  the  sum  of  the  squares  of  the  variations  of  the  individual 
results  from  the  mean. 

In  combining  several  arithmetical  means,  representing  several  series, 
into  one  general  mean,  each  receives  a  weight  inversely  proportional  to 
the  square  of  its  probable  error.  Let  A,  B,  C,  etc.,  be  such  means,  and 
a,  6,  c  their  probable  errors  respectively.  Then  the  general  mean  is  de- 
termined by  the  formula  : 

A       JL  +  _£_. 

(2.)  u  =  ^'-^'^- 


For  the  probable  error  of  this  general  mean  we  have  : 


In  the  calculation  of  atomic  and  molecular  weights  the  following 
formulae  are  used :  Taking,  as  before,  capital  letters  to  represent  known 
quantities,  and  small  letters  for  their  probable  errors  respectively,  we 
have  for  the  probable  error  of  the  sum  or  difference  of  two  quantities, 
A  and  B : 


For  the  product  of  A  multiplied  by  B  the  probable  error  is 
(5.)  e  = 


For  the  product  of  three  quantities,  ABC  : 


T> 

For  a  quotient,  -T'  the  probable  error  becomes 


(7.) 


8  THE    ATOMIC    WEIGHTS. 

Given  a  proportion,  A  :  B  :  :  C  :  x,  the  probable  error  of  the  fourth  term 
is  as  follows : 


This  formula  is  used  in  nearly  every  atomic  weight  calculation,  and 
is,  therefore,  exceptionally  important.  Rarely  a  more  complicated  case 
arises  in  a  proportion  of  this  kind  : 


In  this  proportion  the  unknown  quantity  occurs  in  two  terms.     Its 
probable  error  is  found  by  this  expression,  and  is  always  large  : 


(9.) 


When  several  independent  values  have  been  calculated  for  an  atomic 
weight  they  are  treated  like  means,  and  combined  according  to  formulae 
(2)  and  (3).  Each  final  result  is,  therefore,  to  be  regarded  as  the  general 
or  weighted  mean  of  all  trustworthy  determinations.  This  method  of 
combination  is  not  theoretically  perfect,  but  it  seems  to  be  the  one  most 
available  in  practice. 


OXYGEN. 

The  ratio  between  oxygen  and  hydrogen  is  the  foundation  upon  which 
the  entire  system  of  atomic  weights  is  sustained.  Hence,  the  accuracy 
of  its  determination  has,  from  the  beginning,  been  recognized  as  of  ex- 
treme importance.  A  trifling  error  here  may  become  cumulative  when 
repeated  through  a  moderate  series  of  other  ratios.  But  few  of  the 
elements  have,  so  far,  been  compared  directly  with  th£  unit,  hydrogen ; 
practically  all  of  them  are  referred  to  it  through  the  intervention  of 
oxygen,  and  therefore  the  ratio  in  question  requires  discussion  before 
any  other  can  be  profitably  considered. 

Leaving  out  of  account  the  earliest  researches,  which  now  have  only 
historical  value,  the  first  determinations  to  be  noted  are  those  of  Dulong 
and  Berzelius,*  who,  like  some  of  their  successors,  effected  the  synthesis 
of  water  over  heated  oxide  of  copper.  The  essential  features  of  the 
method  are  in  all  cases  the  same.  Hydrogen  gas  is  passed  over  the  hot 
oxide,  and  the  water  thus  formed  is  collected  and  weighed.  From  this 
weight  and  the  loss  of  weight  which  the  oxide  undergoes,  the  exact  com- 

*  Thomson's  Annals  of  Philosophy,  July,  1821,  p.  50. 


OXYGEN.  9 

position  of  water  is  readily  calculated.  Dulong  and  Berzelius  made  but 
three  experiments,  with  the  following  results  for  the  percentages  of 
oxygen  and  hydrogen  in  water : 

O.  H. 

88.942  11.058 

88.809  11.191 

88.954  11.046 

From  these  figures  we  get,  for  the  atomic  weight  of  oxygen,  the  values — 

16.124 
15-863 
16. 106 


.Mean,  16.031,  db  .057. 

As  the  weighings  were  not  reduced  to  a  vacuum,  this  correction  was 
afterwards  applied  by  Clark,*  who  showed  that  these  syntheses  really 
make  0  =  15.894 ;  or,  in  Berzelian  terms,  if  0  =  100,  H  =  12.583.  The 
value  15.894,  dz  .057  we  may  therefore  take  as  the  true  result  of  Dulong 
and  Berzelius'  experiments,  a  result  curiously  close  to  that  reached  in 
the  latest  and  best  researches. 

In  1842. Dumas f  published  his  elaborate  investigation  upon  the  com- 
position of  water.  The  first  point  was  to  get  pure  hydrogen.  This  gas, 
evolved  from  zinc  and  sulphuric  acid,  might  contain  oxides  of  nitrogen ? 
sulphur  dioxide,  hydrosulphuric  acid,  and  arsenic  hydride.  These  im- 
purities were  removed  in  a  series  of  wash  bottles;  the  H2S  by  a  solution 
of  lead  nitrate,  the  H3As  by  silver  sulphate,  and  the  others  by  caustic 
potash.  Finally,  the  gas  was  dried  by  passing  through  sulphuric  acid, 
or,  in  some  of  the  experiments,  over  phosphorus  pentoxide.  The  copper 
oxide  was  thoroughly  dried,  and  the  bulb  containing  it  was  weighed. 
By  a  current  of  dry  hydrogen  all  the  air  was  expelled  from  the  apparatus, 
and  then,  for  ten  or  twelve  hours,  the  oxide  of  copper  was  heated  to  dull 
redness  in  a  constant  stream  of  the  gas.  The  reduced  copper  was  allowed 
to  cool  in  an  atmosphere  of  hydrogen.  The  weighings  were  made  with 
the  bulbs  exhausted  of  air.  The  following  table  gives  the  results : 

Column  A  contains  the  symbol  of  the  drying  substance ;  B  gives  the 
weight  of  the  bulb  and  copper  oxide ;  C,  the  weight  of  bulb  and  reduced 
copper ;  D,  the  weight  of  the  vessel  used  for  collecting  the  water ;  E,  the 
same,  plus  the  water ;  F,  the  weight  of  oxygen ;  G,  the  weight  of  water 
formed ;  H,  the  crude  equivalent  of  H  when  O  =  10,000 ;  I,  the  equiva- 
lent of  H,  corrected  for  the  air  contained  in  the  sulphuric  acid  employed. 
This  correction  is  not  explained,  and  seems  to  be  questionable. 

*  Philosophical  Magazine,  3d  series,  20,  341. 
fCompt.  Rend.,  14,  537. 


10 


THE   ATOMIC   WEIGHTS. 


vO      O      N '    O    vO      O      coo      •-"      ON     O     oo     oo      N      N      <->      «r^o 

ON     OO       tvON^j-vocoONVOOO*       ON      O°       ^f     NO*       M'       C°N      vo      ^-     Oo' 
h      vo      vo      vo      **t"      vo      ^"      ^t*      vo      vo      vo      vo      T}-      vo      vo      ^* 

vo  O  *i  NO  N  CO  NO  O  CO  *tf-  N  CO  tv  *-  OO  NO  cOvoOO 
O  ON  oc|  O*  NO'  NO'  rf-  O  oo"  O  '-'  co  tv.  06  vo  o  iv,  tv  od 

VO       T  '      vo      vo      vo      vo      vo      vo      vo      vo      vo      vo      vo      vo      vo      lO      vo      Tf 

NNNNNNNNNNN 

tv.  vo  co  rj-  O  tv  OQ  CONO  OOO  N  ONO  tv,  O  OO  vo  tv 
M  OVOTJ-NO  rj-  tv,  CNI  00  N  tv,OO  ONNO  tv,ONvotv,tv. 
00  ONOO  ONO  HHNO  vocoO  noo  covocOTj-i-iNO 
T^-N'  COTJ-VOO^ON"-"  tv,oO*  ONtv.O\Oo'  CO  *-*  00*  NO"  ^f 
HH  N  NNOOO  ThcovoNO  VOVONONO  VONO  ^cococo 

ON?NJ  vOTj-rfi-i  w  tv.i-.OOOO  ONOOO  COOiN  COlv. 
IV.NO  ONQNO  tv«oO  cocoOOO  ONCOOOOONO  COM 
•-"  co^O  covooooo  OCOvorv,ooo  •^t-tv^H  woo 

CO  O'  O'  rv  NO*  CO  rf  vo  O  i-<  N  ON  N  M  \o*  NO"  rj-  M*  o" 
t-i  C>4  W  vorv^-co^-NO  VOVOVONO  vovococococo 

T}-N  TJ-COMNO  N  r^NO  lv.O  O  covoONO  VOIV.ON 
COCONO  M  ONOOC  T}-  ri-  i-i  i-  O  tvio«  cotvcoco 
NO  ^^  tv,  co  ci  c^  ^-  c^  c^  ^  ON  t~v  01  ^h  co  O  r^  oo  vo 

vo  1-1  N*  CO*  CO  NO  oo"  NO"  o'  ON  co  OO*  N  ON  CO  o'  NO*  ^  M* 
ON  »-<  NO  ^J"  tvi  **  tv.  t^,  Q\  ON  co  ON  vo  ON  C4  c^  C^l  c^  M 
Tj-voTl-ONONONOOOQOO  tv.ONONtv.tv-i  ONONONON 

tvi      tv.      **        O        *"*        ON      Tf"       ^-       O        vo      W        tv.       ^"      t*^      C*J        O        tVi      CJ        C^ 

O  C^4  i^  ON  co  vo  O  CN)  NO  ON  co  OO  tv.  o^  NO  ^"  •— »  NO  NO 
OO  M  tvi-i  ro«  "fONONO  OOO  ^coO  tvNOOONOOO 

o'oo     o\Tftv,tv,o\T*-c<i'     «     T^-W*     N"     1-1     ^foo"     tv,oo"     tv 

OOOO  COOOOONO  COM  M  Tt-tvcooo  T^-NO  tvOOOO  tv, 
Tl-Td-TtOOOOOOOOOOOO  tvOO  ONNO  tvOOOOOOOOO 

NDNO       vovoN       vorJ-OO        M       tVitvN       votv.N        COO        M       vo 

OOO      tvMOO      voO      coi-iOO      COONNOOONONO      O      CON 

OO  I™*  I"*         OO  HH  NN  HH  tV.       NO  ^t"         1^  ^         tVi         ^f-         CO        VO         O         NO         GO 

oo*     ^  NO*    od    oo"     o"     tv  NO"     ^f"    o     vo    co  06     o'     IH     ON    o"     tv   o 

tv.csi  ONNO  M  ONMNO  TJ-ONCO«  ONONOO  •-<  N  M  w 
vooo  1-1  ONNONO  vovocovovoO  VOVOVOM  M  M  N 

OO  ^  tv.  N  T^-M  w  (S  ^-N  Tj-00  ION  rJ-VONONO  vo 
ONVONOOO  votv,ONNONO  CONO  NOO  COOO  coi-i  tviNO 

CS      COCONOOO      VONONO      ONNO      VONONONO      ONtvtvtvtv 


w 


OXYGEN.  11 

In  the  sum  total  of  these  nineteen  experiments,  840.161  grammes  of 
oxygen  form  945.439  grammes  of  water.  This  gives,  in  percentages,  for 
the  composition  of  water  —  oxygen,  88.864;  hydrogen,  11.136.  Hence 
the  atomic  weight  of  oxygen,  calculated  in  mass,  is  15.9608.  In  the 
following  column  the  values  are  deduced  from  the  individual  data  given 
under  the  headings  F  and  G  : 


16.014 
16.024 
15-992 
15.916 
15.916 

15.943 
16.000 

15.892 
15-995 
15-984 
15-958 
15.902 

15.987 
15.926 

15.992 
15-904 
15.900 
16.015 

Mean,  15.9607,  with  a  probable  error  of  ±  .0070. 

In  calculating  the  above  column  several  discrepancies  were  noted, 
probably  due  to  misprints  in  the  original  memoir.  On  comparing  col- 
umns B  and  C  with  F,  or  D  and  E  with  G,  these  anomalies  chiefly  ap- 
pear. They  were'  detected  and  carefully  considered  in  the  course  of  my 
own  calculations  ;  and,  I  believe,  eliminated  from  the  final  result. 

The  investigation  of  Erdmann  and  Marchand  *  followed  closely  after 
that  of  Dumas.  The  method  of  procedure  was  essentially  that  of  the 
latter  chemist,  differing  from  it  only  in  points  of  detail.  The  hydrogen 
used  was  prepared  from  zinc  and  sulphuric  acid,  and  the  zinc,  which 
contained  traces  of  carbon,  was  proved  to  be  free  from  arsenic  and  sul- 
phur. The  copper  oxide  was  made  partly  from  copper  turnings  and 
partly  by  the  ignition  of  the  nitrate.  The  results  obtained  are  given  in 
two  series,  in  one  of  which  the  weighings  were  not  actually  made  in 
vacuo,  but  were,  nevertheless,  reduced  to  a  vacuum  standard.  In  the 
second  series  the  copper  oxide  and  copper  were  weighed  in  vacuo.  The 
following  table  contains  the  corrected  weights  of  water  obtained  and  of 
the  oxygen  in  it,  with  the  value  found  for  the  atomic  weight  of  oxygen 
in  a  third  column.  The  weights  are  given  in  grammes. 

*  Journ.  fur  Prakt.  Chem.,  1842,  bd.  26,  s.  461. 


12  THE    ATOMIC    WEIGHTS. 

First  Series. 

Wt.  Water.  Wt.  O.  At.  Wt.  O. 

62.980  55-95°  15-917 

95.612  84.924  15.891 

94.523  84.007  15.977 

35-401  3I-46i  I5.970 


Mean,  15.939,  =b  .014 
Second  Series. 

Wt.  Water.  Wt.  O.  At.  Wt.  O. 

41.664  37.°34  15.996 

44.089  39-J95  16.018 

53.232  47-321  16.011 

55.636  49.460  16.017 

Mean,  16.010,  ±  .0036 

The  effect  of  discussing  these  two  series  separately  is  somewhat  start- 
ling. It  gives  to  the  four  experiments  in  Erdmann  and  Marchand's 
second  group  a  weight  vastly  greater  than  their  other  four  and  Dumas' 
nineteen  taken  together.  For  so  great  a  superiority  as  this  there  is  no 
adequate  reason ;  and  it  is  highly  probable  that  it  is  due  almost  entirely 
to  fortunate  coincidences,  rather  than  to  greater  accuracy  of  work.  We 
will,  therefore,  treat  Erdmann  and  Marchand's  experiments  as  one  series, 
giving  all  equal  weight,  the  mean  now  becoming  0  =  15.975,  zh  .0113. 
If  we  take  the  sum  of  the  eight  experiments,  483.137  grammes  water 
and  429.352  grammes  oxygen,  and  compute  from  these  figures,  then 
O  =  15.966. 

It  would  be  easy  to  point  out  the  sources  of  error  in  the  foregoing  sets 
of  determinations,  but  it  is  hardly  worth  while  to  do  so  in  detail.  A  few 
leading  suggestions  are  enough  for  present  purposes.  First,  there  is  an 
insignificant  error  due  to  the  occlusion  of  hydrogen  by  metallic  copper, 
rendering  the  apparent  weight  of  the  latter  a  trifle  too  high.  Secondly, 
as  shown  by  Dittmar  and  Henderson,  hydrogen  dried  by  passage  through 
sulphuric  acid  becomes  perceptibly  contaminated  with  sulphur  dioxide. 
In  the  third  place,  Morley  *  has  found  that  hydrogen  prepared  from  zinc 
always  contains  carbon  compounds  not  removable  by  absorption  and 
washing.  Erdmann  and  Marchand  themselves  note  that  their  zinc  con- 
tained traces  of  carbon.  Finally,  copper  oxide,  especially  when  pre- 
pared by  the  ignition  of  the  nitrate,  is  very  apt  to  contain  gaseous  impuri- 
ties, and  particularly  occluded  nitrogen. f  Any  or  all  of  these  sources  of 
error  may  have  vitiated  the  three  investigations  so  far  considered,  but  it 
would  be  useless  to  speculate  as  to  the  extent  of  their  influence.  They 

*Amer.  Chetn.  Journ.,  12,  469.     1890. 

f  See  Richards'  work  cited  in  the  chapter  on  copper. 


OXYGEN.  13 

amply  account,  however,  for  the  differences  between  the  older  and  the 
later  determinations  of  the  constant  under  discussion. 

Leaving  out  of  account  all  measurements  of  the  relative  densities  of 
hydrogen  and  oxygen,  to  be  considered  separately  later,  the  next  de- 
termination to  be  noted  is  that  published  by  J.  Thomsen  in  1870.* 
Unfortunately  this  chemist  has  not  published  the  details  of  his  work, 
but  only  the  end  results.  Partly  by  the  oxidation  of  hydrogen  over 
heated  copper  oxide,  and  partly  by  its  direct  union  with  oxygen,  Thom- 
sen finds  that  at  the  latitude  of  Copenhagen,  and  at  sea  level,  one  litre  of 
dry  hydrogen  at  0°  and  760  mm.  pressure  will  form  .8041  gramme  of 
water.  According  to  Regnault,  at  this  latitude,  level,  temperature,  and 
pressure,  a  litre  of  hydrogen  weighs  .08954  gramme.  From  these  data 
O  =  15.9605.  It  will  be  seen  at  once  that  Thomson's  work  depends  in 
great  part  upon  that  of  Regnault,  and  is  therefore  subject  to  the  correc- 
tions recently  applied  by  Crafts  and  others  to  the  latter.  These  cor- 
rections, which  will  be  discussed  further  on,  reduce  the  value  of  O  from 
15.9605  to  15.91.  In  order  to  combine  this  value  with  others,  it  is  neces- 
sary to  assign  it  weight  arbitrarily,  and  as  Thomsen  made  eight  experi- 
ments, which  are  said  to  be  concordant,  it  may  be  fair,  to  rank  his 
determination  with  that  of  Erdmann  and  Marchand,  and  to  assume  for 
it  the  same  probable  error.  The  value  15.91,  ±  .0113  will  therefore  be 
taken  as  the  outcome  of  Thomsen's  research. 

In  1887  Cooke  and  Richards  published  the  results  of  their  elaborate 
investigation.!  These  chemists  weighed  hydrogen,  burned  it  over  copper 
oxide,  and  weighed  the  water  produced.  The  copper  oxide  was  prepared 
from  absolutely  pure  electrolytic  copper,  and  the  hydrogen  was  obtained 
from  three  distinct  sources,  as  follows :  First,  from  pure  zinc  and  hydro- 
chloric acid ;  second,  by  electrolysis,  in  a  generator  containing  dilute 
hydrochloric  acid  and  zinc-mercury  amalgam ;  third,  by  the  action  of 
caustic  potash  solution  upon  sheet  aluminum.  The  gas  was  dried  ancl 
purified  by  passage  through  a  system  of  tubes  and  towers  containing 
potash,  calcium  chloride,  glass  beads  drenched  with  sulphuric  acid,  and 
phosphorus  pentoxide.  No  impurity  could  be  discovered  in  it,  and  even 
nitrogen  was  sought  for  spectroscopically  without  being  found. 

The  hydrogen  was  weighed  in  a  glass  globe  holding  nearly  five  litres 
and  weighing  570.5  grammes,  which  was  counterpoised  by  a  second  globe 
of  exactly  the  same  external  volume.  Before  filling,  the  globe  was  ex- 
hausted to  within  1  mm.  of  mercury  and  weighed.  It  was  then  filled 
with  hydrogen  and  weighed'  again.  The  difference  between  the  two 
weights  gives  the  weight  of  hydrogen  taken. 

In  burning,  the  hydrogen  was  swept  from  the  globe  into  the  combus- 
tion furnace  by  means  of  a  stream  of  air  which  had  previously  been 
passed  over  hot  reduced  copper  and  hot  cupric  oxide,  then  through  potash 

*Berichte  d.  Deutsch.  Chem.  Gesell.,  1870,  s.  928. 
fProc.  Amer.  Acad.,  23,  149.    Am.  Chem.  Journ.,  10,  81. 


14  THE   ATOMIC   WEIGHTS. 

bulbs,  and  finally  through  a  system  of  driers  containing  successively 
calcium  chloride,  sulphuric  acid,  and  phosphorus  pentoxide.  The  water 
formed  by  the  combustion  was  collected  in  a  condensing  tube  connected 
with  a  U  tube  containing  phosphorus  pentoxide.  The  latter  was  fol- 
lowed by  a  safety  tube  containing  either  calcium  chloride  or  phosphorus 
pentoxide,  added  to  the  apparatus  to  prevent  reflex  diffusion.  Full 
details  as  to  the  arrangement  and  construction  of  the  apparatus  are 
given.  The  final  results  appear  in  three  series,  representing  jthe  three 
sources  from  which  the  hydrogen  was  obtained.  All  weights  are  cor- 
rected to  a  vacuum. 

First  Series. — Hydrogen  from  Zinc  and  Acid. 

Wt.  of  H.  Wt.  H.,0.  At.  Wt.  O. 
.4233                          3-8048  15.977 

.4136  3-7094  15.937 

.4213  3-7834  15-960 

.4163  3.7345  15.941 

.413'  3-7085  15-954 


Mean,  15.954,  rh  .0048 

Second  Series. — Electrolytic  Hydrogen. 

.4112  3-6930  15.962 

.4089  3.6709  15-955 

•4261  t   ,     3.8253  15-955 

•4197  3-7651  15-942 

•4H4  3.7I97  J5-953 


Mean,  15.953,  =h  .0022 

Third  Series.— Hydrogen  from  Aluminum. 

.42205  3.7865  15.943 

.4284  3-8436  15-944 

.4205  3-7776  15.967 

•43205  3-8748  15.937 

.4153  3-7281  15.954 

.4167  3-7435  15-967 

Mean,  15.952,  ±  .0035 
Mean  of  all  as  one  series,  15.953,  =t  .°°2O 

Shortly  after  the  appearance  of  this  paper  by  Cooke  and  Richards 
Lord  Rayleigh  pointed  out  the  fact,  already  noted  by  Agamennone,  that 
a  glass  globe  when  exhausted  is  sensibly  condensed  by  the  pressure  of 
the  surrounding  atmosphere.  This  fact  involves  a  correction  to  the  fore- 
going data,  due  to  a  change  in  the  tare  of  the  globe  used,  and  this  cor- 
rection was  promptly  determined  and  applied  by  the  authors.*  By  a 

*  Proc.  Atner.  Acad.,  23,  182.     Am.  Chem.  Journ.,  10,  191. 


OXYGEN.  15 

careful  series  of  measurements  they  found  that  the  correction  amounted 
to  an  average  increase  of  1.98  milligrammes  to  the  weight  of  hydrogen 
taken  in  each  experiment.  Hence  0  equals  not  15.953,  but  15.869,  the 
probable  error  remaining  unchanged.  The  final  result  of  Cooke  and 
Richards'  investigation,  therefore,  is 

O=  15.869,  ±  .0020. 

Reiser's  determinations  of  the  atomic  weight  of  oxygen  were  published 
almost  simultaneously  with  Cooke  and  Richards'.  He  burned  hydrogen 
occluded  by  palladium,  and  weighed  the  water  so  formed.  In  a  pre- 
liminary paper  *  the  following  results  are  given : 

Wt.  of  H.  Wt.  of  ttjO.  At.  Wt.  O. 
.65100                         5-8i777  I5-873 

.60517  5-41540  15.897 

-33733  3-00655  15.822 

Mean,  15.864,  ±  .015 

Not  long  after  the  publication  of  the  foregoing  data  Reiser's  full  paper 
appeared. f  Palladium  foil,  warmed  to  a  temperature  of  250°,  was  satu- 
rated with  hydrogen  prepared  from  dilute  sulphuric  acid  and  zinc  free 
from  arsenic.  From  100  to  140  grammes  of  palladium  were  taken,  and 
it  was  first  proved  that  the  metal  did  not  absorb  other  gases  which  might 
contaminate  the  hydrogen.  Before  charging,  the  foil  was  heated  to  bright 
redness  in  vacuo.  After  charging,  the  tube  containing  the  palladium 
hydride  was  exhausted  by  means  of  a  Geissler  pump  to  remove  any 
nitrogen  which  might  have  been  present.  In  the  preliminary  investiga- 
tion cited  above,  the  latter  precaution  was  neglected,  which  may  account 
for  the  low  results. 

Between  the  palladium  tube  and  the  combustion  tube  a  U  tube  was 
interposed,  containing  phosphorus  pentoxide.  This  was  to  determine 
the  amount  of  moisture  in  the  hydrogen.  The  combustion  tube  was 
filled  with  granular  copper  oxide,  prepared  by  reducing  the  commercial 
oxide  in  hydrogen,  heating  the  metal  so  obtained  to  bright  redness  in  a 
vacuum,  and  then  reoxidizing  with  pure  oxygen. 

Upon  warming  the  palladium  tube,  which  was  first  carefully  weighed, 
hydrogen  was  given  off  and  allowed  to  pass  into  the  combustion  tube. 
When  the  greater  part  of  it  had  been  burned,  the  tube  was  cut  off  by 
means  of  a  stopcock  and  allowed  to  cool.  Meanwhile  a  stream  of  nitro- 
gen was  passed  through  the  combustion  tube,  sweeping  hydrogen  before 
it.  This  was  followed  by  a  current  of  oxygen,  reoxidizing  the  reduced 
copper;  and  the  copper  oxide  was  finally  cooled  in  a  stream  of  dry  air. 
The  water  produced  by  the  combustion  was  collected  in  a  weighed  bulb 
tube,  followed  by  a  weighed  U  tube  containing  phosphorus  pentoxide. 

*  Berichte,  20,  2323.     1887. 

t  Amer.  Chem.  Journ.,  10,  249.     1888. 


16  THE   ATOMIC   WEIGHTS. 

A  second  phosphorus  pentoxide  tube  served  to  prevent  the  sucking  back 
of  moisture  from  the  external  air.  The  loss  in  weight  of  the  palladium 
tube,  corrected  by  the  gain  in  weight  of  the  first  phosphorus  pentoxide, 
gave  the  weight  of  hydrogen  taken.  The  gain  in  weight  of  the  two  col- 
lecting tubes  gave  the  weight  of  water  formed.  All  weights  in  the  follow- 
ing table  of  results  are  reduced  to  a  vacuum : 

Wt.  of  H.  Wt.  H^O.  At.  Wt.  O. 

.34H5  3-06338  15.943 

.68394  6.14000  15.955 

.65529  5.88200  15-9S2 

.65295  5.86206  15.954 

.66664  5.98116  J5«944 

•66647  5-98341  15-955 

.57967  5.20493  I5-958 

.66254  5.94758  15-952 

.87770  7.86775  I5-950 

.77215  6.93036  15.951 


Mean,  15.9514,  ±  .0011. 

In  sum,  6.55880  grammes' of  hydrogen  gave  52.30383  of  water,  whence 
O  =  15.9492. 

In  March,  1889,  Lord  Rayleigh  *  published  a  few  determinations  of  the 
atomic  weight  of  oxygen  obtained  by  still  a  new  method.  Pure  hydrogen 
and  pure  oxygen  were  both  weighed  in  glass  globes.  From  these  they 
passed  into  a  mixing  chamber,  and  thence  into  a  eudiometer,  where  they 
were  gradually  exploded  by  a  series  of  electric  sparks.  After  explosion 
the  residual  gas  remaining  in  the  eudiometer  was  determined  and  meas- 
ured. The  results,  given  without  weighings  or  explicit  details,  are  as 
follows  : 

15.93 
15-98 

15-98 
15-93 
15.92 


Mean,  15.948,  ±.009 

Correcting  this  result  for  shrinkage  of  the  globes  and  consequent  change 
of  tare,  it  becomes  0  =  15.89,  ±  .009. 

In  the  same  month  that  Lord  Rayleigh's  paper  appeared,  Noyes  f  pub- 
lished his  first  series  of  determinations.  His  plan  was  to  pass  hydrogen 
into  an  apparatus  containing  hot  copper  oxide}  condensing  the  water 
formed  in  the  same  apparatus,  and  from  the  gain  in  weight  of  the  latter 
getting  the  weight  of  the  hydrogen  absorbed.  The  apparatus  devised  for 

*Proc.  Roy.  Soc.,  45,  425. 

f  Amer.  Chem.  Journ.,  n,  155.    1889. 


OXYGEN.  17 

this  purpose  consisted  essentially  of  a  glass  bulb  of  30  to  50  cc.  capacity, 
with  a  stopcock  tube  on  one  side  and  a  sealed  condensing  tube  on  the 
other.  In  weighing,  it  was  counterpoised  by  another  apparatus  of  nearly 
the  same  volume  but  somewhat  less  weight,  in  order  to  obviate  reduc- 
tions to  a  vacuum.  After  filling  the  bulb  with  commercial  copper  oxide 
(90  to  150  grammes),  the  apparatus  was  heated  in  an  airbath,  exhausted 
by  means  of  a  Sprengel  pump,  cooled,  and  weighed.  It  was  next  re- 
placed in  the  airbath,  again  heated,  and  connected  with  an  apparatus 
delivering  purified  hydrogen.  When  a  suitable  amount  of  the  latter  had 
been  admitted,  the  stopcock  was  closed,  and  the  heating  continued  long 
enough  to  convert  all  gaseous  hydrogen  within  it  into  water.  The  appa- 
ratus was  then  cooled  and  weighed,  after  which  it  was  connected  with*  a 
Sprengel  pump,  in  order  to  extract  the  small  quantity  of  nitrogen  which 
was  always  present.  The  latter  was  pumped  out  into  a  eudiometer, 
where  it  was  measured  and  examined.  The  gain  in  weight  of  the  appa- 
ratus, less  the  weight  of  this  very  slight  impurity,  gave  the  weight  of 
hydrogen  oxidized. 

The  next  step  in  the  process  consisted  in  heating  the  apparatus  to  expel 
water,  and  weighing  again.  After  this,  pure  oxygen  was  admitted  and 
the  heating  was  resumed,  so  as  to  oxidize  the  traces  of  hydrogen  which 
had  been  retained  by  the  copper.  Again  the  apparatus  was  cooled  and 
weighed,  and  then  reheated,  when  the  water  formed  was  received  in  a 
bulb  filled  with  phosphorus  pentoxide,  and  the  gaseous  contents  were 
collected  in  a  eudiometer.  On  cooling  and  weighing  the  apparatus,  the 
loss  of  weight,  less  the  weight  of  gases  pumped  out,  gave  the  amount  of 
water  produced  by  the  traces  of  residual  hydrogen  under  consideration. 
This  weight,  added  to  the  loss  of  weight  when  the  original  water  was 
expelled,  gives  the  weight  of  oxygen  taken  away  from  the  copper  oxide. 
Having  thus  the  weight  of  hydrogen  and  the  weight  of  oxygen,  the 
atomic  weight  sought  for  follows.  Six  results  are  given,  but  as  they  are 
repeated,  with  corrections,  in  Noyes'  second  paper,  they  need  not  be 
considered  now. 

Noyes'  methods  were  almost  immediately  criticised  by  Johnson,*  who 
suggested  several  sources  of  error.  This  chemist  had  already  shown  in 
an  earlier  paper  f  that  copper  reduced  in  hydrogen  persistently  retains 
traces  of  the  latter,  and  also  that  when  the  reduction  is  effected  below 
700°,  water  is  retained  too.  The  possible  presence  of  sulphur  in  the 
copper  oxide  was  furthermore  mentioned.  Errors  from  these  sources 
would  tend  to  make  the  apparent  atomic  weight  of  oxygen  too  low. 

In  his  second  paper  J  Noyes  replies  to  the  foregoing  criticisms,  and 
shows  that  they  carry  no  weight,  at  least  so  far  as  his  work  is  concerned. 
He  also  describes  a  number  of  experiments  in  which  oxides  other  than 
copper  oxide  were  tried,  but  without  distinct  success,  and  he  gives  fuller 

*Chem.  News,  59,  272. 

f  Journ.  Chem.  Soc.,  May,  1879. 

jAmer.  Chem.  Journ.,  12,  441.     1890. 


18  THE    ATOMIC    WEIGHTS. 

details  as  to  manipulations  and  materials.     His  final  results  are  in  four 
series,  as  follows : 

First  Series. — Hydrogen  from  Zinc  and  Hydrochloric  Acid. 

WL  of  H.  Wt.  of  O.  At.  Wt.  O. 

•9443                            7-5000  15.885 

.6744                            5-3555  15-882 

.7866                             6.2569  I5-9°9 

•5521                              4.3903  15.904 

.4274                             3-3997  15-909 

.8265                             6.5686  15-895 

Mean,  15.8973,^.0032. 
•  > 

This  series  appeared  in  the  earlier  paper,  but  with  an  error  which  is 
here  corrected. 

Second  Series. — Electrolytic  Hydrogen,  Dried  by  Phosphorus  Pentoxide. 

Wt.  of  H.                    Wt.  of  O.  At.  Wt.  O. 

.5044                          4.0095  15-898 

•6325                           5-0385  15-932 

.6349                           5-°5i7  15-913 

.5564                           4.4175  15-879 

•7335                            5-8224  15.876 

5.3181  15.885 


Mean,  15.8971,^.0064. 

Third  Series. — Electrolytic  Hydrogen,  Dried  by  Passage   Through  a   Tube 

Packed  with  Sodium  Wire. 

Wt.  of  H.  Wt.  of  O.  At.  Wt.  O. 

.9323                           7.4077  15-891 

•9952                          7-9045  15  885 

.3268                          2.5977  15.898 

.7907                          6.2798  15.884 

.7762                          6.1671  15.891 

1.1221  8.9131  15-887 


Mean,  15.8893,  i .0014 

At  the  end  of  this  series  it  was  found  that  the  hydrogen  contained  a 
trace  of  water,  estimated  to  be  equivalent  to  an  excess  of  three  milli- 
grammes in  the  total  h}^drogen  of  the  six  experiments.  Correcting  for 
this,  the  mean  becomes  0  =  15.899. 

Fourth  Series. — Electrolytic  Hydrogen,  Dried  over  Freshly  Sublimed  Phos- 
phorus Pentoxide. 

Wt.  of  H.  Wt.  of  O.  At.  Wt.  O. 

1.0444  8.3017  15-898 

.7704  6.1233  15.896 

.8231  6.5421  15.896 

.8872  7.0490  15.890 

•9993  7-9403  15-892 

1.1910  9.4595  15.885 

Mean,  15.8929,  ±  .0013 


OXYGEN.  19 

The  mean  of  all  the  twenty-four  determinations,  taken  as  one  series, 
with  the  correction  to  the  third  series  included,  is  0  =  15.8966,  ±  .0017. 
In  sum,  there  were  consumed  18.5983  grammes  of  hydrogen  and  147.8145 
of  oxygen  ;  whence  0  =  15.8955. 

Dittmar  and  Henderson,*  who  effected  the  synthesis  of  water  over 
copper  oxide  by  what  was  essentially  the  old  method,  begin  their  memoir 
with  an  exhaustive  criticism  of  the  work  done  by  Dumas  and  by  Erd- 
mann  and  Marchand.  They  show,  as  I  have  already  mentioned,  that 
hydrogen  dried  by  sulphuric  acid  becomes  contaminated  with  sulphur 
dioxide,  and  also  that  a  gas  passed  over  calcium  chloride  may  still  retain 
as  much  as  one  milligramme  of  water  per  litre.  Fused  caustic  potash 
they  found  to  dry  a  gas  quite  completely. 

In  their  first  series  of  syntheses,  Dittmar  and  Henderson  generated 
their  hydrogen  from  zinc  and  acid,  sometimes  hydrochloric  and  some- 
times sulphuric,  and  dried  it  by  passage,  first  through  cotton  wool,  then 
through  vitrioled  pumice,  then  over  red-hot  metallic  copper  to  remove 
oxygen.  In  later  experiments  it  first  traversed  a  column  of  fragments 
of  caustic  soda  to  remove  antimony  derived  from  the  zinc.  The  oxide 
of  copper  used  was  prepared  by  heating  chemically  pure  copper  clip- 
pings in  a  muffle,  and  was  practically  free  from  .sulphur.  In  weighing 
the  several  portions  of  apparatus  it  was  tared  with  somewhat  lighter 
similar  pieces  of  as  nearly  as  possible  the  same  displacement.  The  re- 
sults of  this  series  of  experiments,  which  are  vitiated  by  the  presence, 
unsuspected  at  first,  of  sulphur  dioxide  in  the  hydrogen,  are  stated  in 
values  of  H  when  0  =  16,  but  in  the  following  table  .have  been  recalcu- 
lated to  the  usual  unit : 

Wt.  of  Water.  Wt.  of  O.  At.  Wt.  O. 

4.7980  4.26195  I5-901 

7.55025          6.71315  16.039 

6.2372          5-53935  15.875 

11.29325  10.03585  J5-963 

11.6728  10.3715  I5-940 

11.8433  10.5256  15.976 

11.7317  10.4243  15-947 

19.2404  17.0926  15.916 

20.83435  18.5234  16.031 

17.40235  15.4598  I5-9I7 

19.2631  i7."485  x5-934 

Mean,  15.949,  =b  .0103. 

Reducing  to  a  vacuum,  this  becomes  15.843,  while  a  correction  for  the 
sulphur  dioxide  estimated  to  be  present  in  the  hydrogen  brings  the  value 

*  Proc.  Roy.  Soc.  Glasgow,  22,  33.     Communicated  Dec.  17,  1890. 


20  THE    ATOMIC    WEIGHTS. 

up  again  to  15.865.  Still  another  correction  is  suggested,  namely,  that 
as  the  reduced  copper  in  the  combustion  tube,  before  weighing,  was  ex- 
posed to  a  long-continued  current  of  dry  air,  it  may  have  taken  up  traces 
of  oxygen  chemically,  thereby  increasing  its  weight.  As  this  correction, 
however,  is  quantitatively  uncertain,  it  may  be  neglected  here,  and  the 
result  of  this  series  will  be  taken  as  0  =  15.865,  ±  .0103.  Its  weight, 
relatively  to  some  other  series  of  experiments,  is  evidently  small. 

In  their  second  and  final  series  Dittmar  and  Henderson  dried  their 
hydrogen,  after  deoxidation  by  red-hot  copper,  over  caustic  potash  and 
subsequently  phosphorus  pentoxide.  The  copper  oxide  and  copper  of 
the  combustion  tube  were  both  weighed  in  vacuo.  The  results  were  as 
follows,  vacuum  weights  being  given : 

Wt.  Water.  Wt.  O.  At.  Wt.  O. 

19.2057  17-0530  15.843 

19-5211  17-3342  [15-853] 

19.4672  17.2882  15.868 

22.9272  20.3540  15.820 

23.0080  20.4421  [15.934] 

23.4951  26.8639  15.859 

23.5612  20.9226  [15-859] 

23.7542     ^  21.0957  15.870 

23.6568  21.8994  15.884 

23.6179  21.8593  15.848 

24.6021  21.8499  15.878 

24.3047  21.5788  15.832 

23.6172  20.9709  15.849 


Mean,  15.861,^.0052. 

The  authors  reject  the  three  bracketed  determinations,  because  of 
irregularities  in  the  course  of  the  experiments.  The  mean  of  the  ten 
remaining  determinations  is  15.855,  ±  .0044.  Both  means,  however, 
have  to  be  corrected  for  the  minute  trace  of  hydrogen  occluded  by  the 
reduced  copper.  This  correction,  experimentally  measured,  amounts  to 
-|-  .006.  Hence  the  mean  of  all  the  experiments  in  the  series  becomes 
15.867,  ±  .0052,  and  of  the  ten  accepted  experiments,  15.861,  ±  .0044. 
The  authors  themselves  select  out  seven  experiments,  giving  a  corrected 
mean  of  15.866,  which  they  regard  as  the  best  value.  Taking  all  their 
evidence,  their  two  series  combine  thus : 

First  series 15.865,    ±  .0103 

Second  series 15.867,    ±.0052 

General  mean 15.8667,  ±  .0046 

Leduc,*  who  also  effected  the  synthesis  of  water  over  copper  oxide, 

*  Compt.  Rend.,  115,  41.     1892. 


OXYGEN.  21 

following  Dumas'  method  with  slight  modifications,  gives  the  results  of 
only  two  experiments,  as  follows  : 

Wt.  Water.  Wt.  O.  At.  Wt.  O. 

22.1632  19.6844  15.882 

19.7403  17.5323  15-880 


Mean,  15.881 

These  experiments  we  may  arbitrarily  assign  equal  weight  with  two 
in  Dittmar  and  Henderson's  later  series,  when  the  result  becomes 
15.881,  =b  .0132,  the  value  to  be  accepted.  Leduc  states  that  his  copper 
oxide,  which  was  reduced  at  as  low  a  temperature  as  possible,  was  pre- 
pared by  heating  clippings  of  electrolytic  copper  in  a  stream  of  oxygen. 

To  E.  W.  Morley  *  we  owe  the  first  complete  quantitative  syntheses  of 
water,  in  which  both  gases  were  weighed  separately,  and  afterwards  in 
combination.  The  hydrogen  was  weighed  in  palladium,  as  was  done  by 
Keiser,  and  the  oxygen  was  weighed  in  compensated  globes,  after  the 
manner  of  Regnault.  The  globes  were  contained  in  an  artificial  "  cave," 
to  protect  them  from  moisture  and  from  changes  of  temperature;  being 
so  arranged  that  they  could  be  weighed  by  the  method  of  reversals  with- 
out opening  either  the  "  cave  "  or  the  balance  case.  For  each  weighing 
of  hydrogen  about  600  grammes  of  palladium  were  employed.  After 
weighing,  the  gases  were  burnt  by  means  of  electric  sparks  in  a  suitable 
apparatus,  from  which  the  unburned  residue  could  be  withdrawn  for 
examination.  Finally,  the  apparatus  containing  the  water  produced  was 
closed  by  fusion  and  also  weighed.  Rubber  joints  were  avoided  in  the 
construction  of  the  apparatus,  and  the  connections  were  continuous 
throughout.  The  weights  are  as  follows  : 

H  taken  O  taken.  H^O  formed. 


3-2645 

25.9*76 

29.1788 

3.2559 

25-8531 

29.1052 

3.8193 

30.3210 

34-1389 

3-8450 

3o.5294 

Lost 

3.8382 

30.4700 

34.3151 

3.8523 

30.5818 

34.4327 

3.8298 

30-40  1  3 

34.2284 

3.8286 

30.3966 

34.2261 

•3.8225 

30-3497 

34  1742 

3.8220 

30.3479 

34-1743 

3.7637 

29.8865 

33.6540 

3.8211 

30-3429 

34.1559 

*  "  On  the  Density  of  Oxygen  and  Hydrogen,  and  on  the  Ratio  of  their  Atomic  Weights,"  by 
Edward  W.  Morley.  Smithsonian  Contributions  to  Knowledge,  1895,  4to,  xi  +  .117  pp.,  40  cuts. 
Abstract  in  Am.  Chem.  Journ.,  17,  267  (gravimetric),  and  Ztschr.  Phys.  Chem.,  17,  87  (gaseous  densi- 
ties) ;  also  note  in  Am.  Chem.  Journ.,  17,  396.  Preliminary  notice  in  Proc.  Amer.  Association, 
1891,  p.  185. 


22  THE    ATOMIC    WEIGHTS. 

Hence  we  have — 

H :  O  Ratio  H-.H^O  Ratio. 

15-878  17.877 

15.881  I7.878 

15-878  17.873 

15.880  

15.877  17.881 

15-877  17-876 

15.877  17-875 

15-878  17.879 

15-879  17.881 

15-881  17.883 

15.881  17.883 
15-882  17.878 


Mean,  15.8792,  ±  .00032  Mean,  17.8785,  ±  .00066 

Combined,  these  data  give : 

From  ratio  H2 :  O  .      O  —  15.8792,  ±  .00032 

"     H2:H20 0^15.8785,^.00066 

General  mean O  —  15.8790,  =b  .00028 

For  details,  Morley's  fall  paper  must  be  consulted.  No  abstract  can 
do  justice  to  the  remarkable  work  therein  recorded. 

Two  other  series  of  determinations,  by  Julius  Thomsen,  remain  to  be 
noticed.  In  the  earlier  paper  *  he  determined  the  ratio  between  HC1 
and  NH3,  and  thence,  using  Stas'  values  for  Cl  and  N,  fixed  by  reference 
to  0  =  16,  computed  the  ratio  H  :  0.  This  method  was  so  indirect  as  to 
be  of  little  importance,  and  gave  for  the  atomic  weight  of  oxygen  approxi- 
mately the  round  number  16.  I  shall  use  the  data  farther  on  in  cal- 
culating the  atomic  weight  of  nitrogen.  The  paper  has  been  sufficiently 
criticised  by  Meyer  and  Seubert,f  who  have  discussed  its  sources  of  error. 

In  Thomsen's  later  paper  J  a  method  of  determination  is  described 
which  is,  like  the  preceding,  quite  novel,  but  more  direct.  First,  alu- 
minum, in  weighed  quantities,  was  dissolved  in, caustic  potash  solution. 
In  one  set  of  experiments  the  apparatus  was  so  constructed  that  the 
hydrogen  evolved  was  dried  and  then  expelled.  The  loss  of  weight  of 
the  apparatus  gave  the  weight  of  the  hydrogen  so  liberated.  In  the 
second  set  of  experiments  the  hydrogen  passed  into  a  combustion 
chamber  in  which  it  was  burned  with  oxygen,  the  water  being  retained. 
The  increase  in  weight  of  this  apparatus  gave  the  weight  of  oxygen  so 
taken  up.  The  two  series,  reduced  to  the  standard  of  a  unit  weight  of 
aluminum,  gave  the  ratio  between  oxygen  and  hydrogen. 

*Zeitsch.  Physikal.  Chem.,  13,  398.     1894. 

fBer.,  27,  2770. 

I  Zeitsch.  Anorg.  Chem.,  :r,  14.     1895. 


OXYGEN.  23 

The  results  of  the  two  series,  reduced  to  a  vacuum  and  stated  as  ratios, 
are  as  follows : 

First.  Second. 

Weight  of  H  Weight  of  O 

Weight  of  Al'  Weight  of  Al* 

o.iuSo  0.88788 

0.11175  0.88799 

0.11194  0.88774 

0.11205  0.88779 

0.11189  0.88785 

o.i i 200  0.88789 

0.11194  0.88798 

0.11175  0.88787 

0.11190  0.88773 

0.11182  0.88798 

0.11204  0.88785 

o.i  1 202 

0.11204  0.88787,^0.000018 

0.11179 

0.11178 

O.I 1202 

0.11188 
0.11186 
0.11185 
o.i  1 190 
0.11187  1 


0.11190,  ±  0.000015 

Dividing  the  mean  of  the  second  column  by  the  mean  of  the  first,  we 
have  for  the  equivalent  of  oxygen  : 

0.88787,  ±  0.000018 


0.11190,  ±0.000015 
Hence  0  ==  15.8690,  ±  0.0022. 


=  7-9345,  ±0.0011 


The  details  of  the  investigation  are  somewhat  complicated,  and  involve 
various  corrections  which  need  not -be  considered  here.  The  result  as 
stated  includes  all  corrections  and  is  evidently  good.  The  ratios,  how- 
ever, cannot  be  reversed  and  used  for  measuring  the  atomic  weight  of 
aluminum,  because  the  metal  employed  was  not  absolutely  pure. 

We  have  now  before  us,  representing  syntheses  of  water,  thirteen  series, 
as  follows : 

Dulong  and  Berzelius O  =  15.894,    ±  .057 

Dumas ..  .  15.9607,  ±  .0070 

Erdmann  and  Marchand l5-975,    ±.0113 

Thomsen,  1870 15.91,      ±.0113 

Cooke  and  Richards 15.869,    ±  .0020 

Reiser,  1887 15.864,     ±  .015 

1888 15.9514,  ±  .0011 


24  THE    ATOMIC   WKIGHTS. 

Rayleigh 15.89,      ±  .009 

Noyes 15.8966,^.0017 

Dittmar  and  Henderson 15.8667,  ±  .0046 

Leduc 15.881,    d=  .0132 

M.orley 15.8790,  ±  .00028 

Thomson,  1895 15.8690,  ±  .0022 

General  mean O  =  15.8837,  ±  .00026 

Rejecting  Keiser 1 5. 8796,  ±  .00027 

If  we  reject  all  except  the  determinations  of  Cooke  and  Richards,  Ray- 
leigh, Noyes,  Dittmar  and  Henderson,  Leduc,  Thomsen,  and  Moiiey,  the 
general  mean  of  these  becomes  15.8794,  ±  .00027.  From  this  it  is  evi- 
dent that  Reiser's  determinations  alone,  among  the  higher  values  for  0. 
carry  any  appreciable  weight :  and  it  also  seems  clear  that  the  rounded- 
off  number,  O  ==  15.88,  ±  .0003,  cannot  be  very  far  from  the  truth;  at 
least  so  far  as  the  synthetic  evidence  goes. 


In  discussing  the  relative  densities  of  oxygen  and  hydrogen  gases  we 
need  consider  only  the  more  modern  determinations,  beginning  with 
those  of  Dumas  and  Boussingault.  As  the  older  work  has  some  his- 
torical value,  I  may  in  passing  just  cite  its  results.  For  the  density  of 
hydrogen  we  have  .0769,  Lavoisier;  .0693,  Thomson;  .092,  Cavendish; 
.0732,  Biot  and  Arago ;  .0688,  Dulong  and  Berzelius.  For  oxygen  there 
are  the  following  determinations:'  1.087,  Fourcroy,  Vauquelin,  and  Se- 
guin;  1.103,  Kirwan;  1.128,  Davy;  1,088,  Allen  and  Pepys  ;  1.1036,  Biot 
and  Arago;  1.1117,  Thomson;  1.1056,  De  Saussure;  1.1026,  Dulong  and 
Berzelius;  1.106,  Buff;  1.1052,  Wrede.* 

In  1841  Dumas  and  Boussingault  f  published  their  determinations  of 
gaseous  densities.  For  hydrogen  they  obtained  values  ranging  from  .0691 
to  .0695 ;  but  beyond  this  mere  statement  they  give  no  details.  For 
oxygen  three  determinations  were  made,  with  the  following  results : 

'.1055 

1.1058 


Mean,  1.10567,  ±  .00006 

If  we  take  the  two  extreme  values  given  above  for  hydrogen,  and  re- 
gard them  as  the  entire  series,  they  give  us  a  mean  of  .0693,  ±  .00013. 
This  mean  hydrogen  value,  combined  with  the  mean  for  oxygen,  gives 
for  the  latter,  when  H  =  1,  the  density  ratio  15.9538,  ±  .031. 

Regnault's  researches,  published  four  years  later,  J  were  much  more 

*  For  Wrede's  work,  see  Berzelius'  Jahresbericht  for  1843.  For  Dulong  and  Berzelius,  see  the 
paper  already  cited.  All  the  other  determinations  are  taken  from  Gmelin's  Handbook,  Caven- 
dish edition,  v.  i,  p.  279. 

f  Compt.  Rend.,  12,  1005.     Compare  also  with  Dumas,  Compt.  Rend.,  14,  537. 

J  Compt.  Rend.,  20,  975. 


OXYGEN.  25 

elaborately  executed.  Indeed,  they  have  long  stood  among  the  classics 
of  physical  science,  and  it  is  only  recently  that  they  have  been  sup- 
planted by  other  measurements. 

For  hydrogen   three   determinations  of  density  gave  the  following 
results : 

.06923 

.06932 

.06924 


Mean,  .069263,  ±  .000019 

For  oxygen  four  determinations  were  made,  but  in  the  first  one  the 
gas  was  contaminated  by  traces  of  hydrogen,  and  the  value  obtained, 
1.10525,  was,  therefore,  rejected  by  Regnault  as  too  low.  The  other  three 
are  as  follows : 

1.10561 

1.10564 

1.10565 

Mean,  1.105633,  ±  .000008 

Now,  combining  the  hydrogen  and  oxygen  series,  we  have  the  ratio 
H  :  0  :  :  1  :  15.9628,  ±  .0044.  According  to  Le  Conte,*  Regnault's  reduc- 
tions contain  slight  numerical  errors,  which,  corrected,  give  for  the  density 
of  oxygen,  1.105612,  and  for  hydrogen,  .069269.  Ratio,  1  :  15.9611. 

A  much  weightier  correction  to  Regnault's  data  has  already  been  in- 
dicated in  the  discussion  of  Cooke  and  Richards'  work.  He  assumed 
that  the  globes  in  which  the  gases  were  weighed  underwent  no  changes 
of  volume,  but  Agamennone,f  and  after  him,  but  independently,!  Lord 
Rayleigh  showed  that  an  exhausted  vessel  was  perceptibly  compressed 
by  atmospheric  pressure.  Hence  its  volume  when  empty  was  less  than 
its  volume  when  filled  with  gas.  Crafts,  having  access  to  Regnault's 
original  apparatus,  has  determined  the  magnitude  of  the  correction  indi- 
cated^ Unfortunately,  the  globe  actually  used  by  Regnault  had  been 
destroyed,  but  another  globe  of  the  same  lot  was  available.  With  this 
the  amount  of  shrinkage  during  exhaustion  was  measured,  and  Reg- 
iiault's  densities  were  thereby  changed  to  1.10562  for  oxygen,  and 
.06949  for  hydrogen.  Corrected  ratio,  1  :  15.9105.  Doubtless  Dumas 
and  Boussingault's  data  are  subject  to  a  similar  correction,  and  if  we 
assume  that  it  is  proportionally  the  same  in  amount,  the  ratio  derived 
from  their  experiments  becomes  1  :  15.9015. 

In  the  same  paper,  that  which  contained  the  discovery  of  this  correc- 
tion, Lord  Rayleigh  gives  a  short  series  of  measurements  of  his  own. 

*  Private  communication.     See  also  Phil.  Mag.  (4),  27,  29,  1864,  and  Smithsonian  Report,  1878, 
p.  428. 

f  Atti  Rendiconti  Acad.  I^incei,  1885. 
t  Proc.  Roy.  Soc.,  43,  356.  Feb.,  1888. 
g  Conipt.  Rend.,  106,  1662. 


26 


THE   ATOMIC   WEIGHTS. 


His  hydrogen  was  prepared  from  zinc  and  sulphuric  acid,  and  was  puri- 
fied by  passage  over  liquid  potash,  then  through  powdered  mercuric 
chloride,  and  then  through  pulverized  solid  potash.  It  was  dried  by 
means  of  phosphorus  pentoxide.  His  oxygen  was  derived  partly  from 
potassium  chlorate,  and  partly  from  the  mixed  chlorates  of  sodium  and 
potassium.  Equal  volumes  of  the  two  gases  weighed  as  follows  : 


H. 

.15811 

.15807 
.15798 
•I5792 


O. 

2.5186,     4;    .00061* 


Mean,  .15802,  ±  000029. 

Corrected  for  shrinkage  of  the  exhausted  globe  these  become — H, 
0.15860  ;  O,  2.5192.  Hence  the  ratio  1  :  15.884,  ±  .0048. 

In  1892  Rayleigh  published  a  much  more  elaborate  determination  of 
this  ratio. f  The  gases  were  prepared  electroly tically  from  caustic  potash , 
and  dried  by  means  of  solid  potash  and  phosphorus  pentoxide.  The 
hydrogen  was  previously  passed  over  hot  copper.  The  experiments, 
stated  like  the  previous  series,  are  in  five  groups  ;  two  for  oxygen  and 
three  for  hydrogen;  but  for  present  purposes  the  similar  sets  may  be 
regarded  as  equal  in  weight,  and  so  discussable  together.  The  weights 
of  equal  volumes  are  as  follows : 


H.                                                     O. 

(  -15807                                              2.5182  1 

_.  15816                                                      2.5173 

First  set 

.15811                                                      2.5172 

First  set. 

Mean,  .15808    I    .15803                                                    2.5193 

Mean,  2.51785. 

.15801                                                      2.5174 

L  -15809                                    2.5177 

f  .15800                                    2.5183  ' 

Second  set       '*&2Q                                                 2'5l68 

Second  set. 

Mean,  .15797 

.15792                                                      25172 
.15788                                                      2.5181 

Mean,  2.5172. 

.15783                                                    2.5156 

r  .15807 

.15801                                        Mean,  2.5176, 

±  .00019. 

.15817 

Third  set  j   .1579° 

Mean,  .15804 

.15810 

.15798 

.15802 

1.15807 

Mean,  .15804,  ±  .000019. 

*  Arbitrarily  assigned  the  probable  error  of  a  single  experiment  in  Rayleigh's  paper  of  1892. 
tProc.  Roy.  Soc.,  50,  448,  Feb.  18,  1892. 


OXYGEN.  27 

These  weights  with  various  corrections  relative  to  temperatures  and 
pressures,  and  also  for  the  compression  of  the  exhausted  globe,  ulti- 
mately become  for  H,  .158531 ;  and  for  0,  2.51777.  Hence  the  ratio 
1  :  15.882,  HZ  .0023.  For  details  relative  to  corrections  the  original 
memoir  should  be  consulted. 


In  his  paper  "  On  a  new  method  of  determining  gas  densities,"  *  Cooke 
gives  three  measurements  for  hydrogen,  referred  to  air  as  unity.  They 
are : 

.06957 

.06951 

.06966 


Mean,  .06958,  ih  .000029 

Combining  this  with  Regnault's  density  for  oxygen,  as  corrected  by 
Crafts,  1.10562,  ±  .000008,  we  get  the  ratio  H  :  0  :  :  1  : 15.890,*  ±  .0067. 

Leduc,  working  by  Regnault's  method,  somewhat  modified,  and  cor- 
recting for  shrinkage  of  exhausted  globes,  gives  the  following  densities  :  t 

H.  O. 

.06947  1.10501 

.06949  1.10516 
.06947 


Mean,  .06948,  =b  .00006745 

The  two  oxygen  measurements  are  the  extremes  of  three,  the  mean 
being  1.10506,  ±  .0000337.  Hence  the  ratio  1 :  15.905,  ±  .0154. 

The  first  two  hydrogen  determinations  were  made  with  gas  produced 
by  the  electrolysis  of  caustic  potash,  while  the  third  sample  was  derived 
from  zinc  and  sulphuric  acid.  The  oxygen  was  electrolytic.  Both  gases 
were  passed  over  red-hot  platinum  sponge,  and  dried  by  phosphorus 
pentoxide. 

Much  more  elaborate  determinations  of  the  two  gaseous  densities  are 
those  made  by  Morley.  J  For  oxygen  he  gives  three  series  of  data ;  two 
with  oxygen  from  potassium  chlorate,  and  one  with  gas  partly  from  the 
same  source  and  partly  electrolytic.  In  the  first  series,  temperature  and 
pressure  were  measured  with  a  mercurial  thermometer  and  a  mano- 
barometer.  In  the  second  series  they  were  not  determined  for  each 
experiment,  but  were  fixed  by  comparison  with  a  standard  volume  of 
hydrogen  by  means  of  a  differential  manometer.  In  the  third  series  the 
gas  was  kept  at  the  temperature  of  melting  ice,  and  the  mano-barometer 

*  Proc.  Amer.  Acad.,  24,  202.     1889.    Also  Am.  Chem.  Journ.,  11,  509. 

fCompt.  Rend.,  113,  186.     1891. 

I  Paper  already  cited,  under  the  gravimetric  portion  of  this  chapter. 


28 


THE    ATOMIC    WEIGHTS. 


alone  was  read.     The  results  for  the  weight  in  grammes,  at  latitude  45' 
of  one  litre  of  oxygen  are  as  follows : 


First  Series. 


Second  Series. 


.42864 

[.42952 

.42849 

.42900 

.42838 

.42863 

.42900 

.42853 

.42907 

.42858 

.42887 

.42873 

.42871 

.42913 

.42872 

.42905 

.42883 

.42896 

.42880 

Mean, 

.42875,  ±  .000051 

.42874 

Corrected,* 

.42879,  zh  .OOOO5I 

.42878 

.42872 

.42859 

.            ] 

.42851 

Third  Series. 

.42920 

.42860 

.42906 

.42957 

.42910 

.42930 

.42945 

.42932 

.42908 

.42910 

•42951 

.42933 

.42905 

.42914 

.42849 

.42894 

.000048 

.42886 

000048 

Mean, 

.42912,  zfc 

.000048 

Corrected, 

.42917,  ± 

.000048 

Mean,  1.42882,  ± 
Corrected,  1.42887,  ± 


General  mean  of  all  three  series,  1.42896,  ±  .000028. 

Morley  himself,  for  experimental  reasons,  prefers  the  last  series,  and 
gives  it  double  weight,  getting  a  mean  density  of  1.42900.  The  differ- 
ence between  this  mean  and  that  given  above  is  insignificant  with  ref- 
erence to  the  atomic  weight  problem. 

In  the  case  of  hydrogen,  Morley 's  determinations  fall  into  two  groups, 
but  in  both  the  gas  was  prepared  by  the  electrolysis  of  pure  dilute  sul- 
phuric acid,  and  was  most  elaborately  purified.  In  the  first  group  there 
are  two  series  of  measurements.  Of  these,  the  first  involved  the  reading 
of  temperature  and  pressure  by  means  of  a  mercurial  thermometer  and 
mano-barometer.  In  the  second  series,  the  gas  was  delivered  into  the 
weighing  globes  after  occlusion  in  palladium  ;  it  was  then  kept  at  the 
temperature  of  melting  ice,  and  only  the  syphon  barometer  was  read. 
In  this  group  the  hydrogen  was  possibly  contaminated  with  mercurial 
vapor,  and  the  results  are  discarded  by  Morley  in  his  final  summing  up. 
For  present  purposes,  however,  it  is  unnecessary  to  reject  them,  for  they 
have  confirmatory  value,  and  do  not  appreciably  affect  the  final  mean. 
The  weight  of  one  litre  of  hydrogen  at  45°  latitude,  as  found  in  these  two 
sets  of  determinations,  is  as  follows  : 


*  Correction  applied  by  Morley  to  all  his  series,  for  a  slight  error, 
standard  metre  bar. 


,  in  the  length  of  his 


OXYGEN.  29 


First  Series.  Second  Series. 

.089904  .089977 

.089936  .089894 

.089945  .089987 

.089993  .089948 

.089974  .089951 

.089941  .089960 

.089979  .090018 

.089936  .089909 

.089904  .089953 

.089863  .089974 

.089878  .089922 

.089920  .090093 

.089990  .090007 

.089926  .089899 

.089928  .089974 

.089900 

Mean,  .089934,  ±  .000007               .089869 

Corrected,  .089938,  ±  .000007  .090144 

.089984 


Mean,  .089967,  ±  .000011 
Corrected,  .089970,  d=  .000011 

In  the  second  group  of  experiments,  the  hydrogen  was  weighed  in 
palladium  before  transfer  to  the  calibrated  globe ;  and  in  weighing,  the 
palladium  tube  was  tared  by  a  similar  apparatus  of  nearly  equal  volume 
and  weight.  After  transfer,  which  was  effected  without  the  intervention 
of  stopcocks,  the  volume  and  pressure  of  the  gas  were  taken  at  the 
temperature  of  melting  ice.  A  preliminary  set  of  measurements  was 
made,  followed  by  three  regular  series ;  of  these,  the  first  and  second 
were  with  the  same  apparatus,  and  are  different  only  in  point  of  time, 
a  vacation  falling  between  them.  The  last  series  was  with  a  different 
apparatus.  The  data  are  as  follows,  with  the  means  as  usual : 

Preliminary.  Third  Series.         Fourth  Series.        Fifth  Series. 

.089946  .089874  .089972  .089861 

.089915  .089891  .089877  .089877 

.089881  .089886  .089867  .089870 

.089901  .089866  .089916  .089867 

.089945  .089911  .089770  .089839 

.089856  .089846  .089874 

Mean,  .089918,  .089912  .089864 

±  .0000271  .089872  Mean,  .089875,  .089883 

Corrected,  .089921  =b  .0000187  .089830 

Mean,  .089883,    Corrected,  .089880  .089877 

±  .0000049  .089851 

Corrected,  .089886 

Mean,  .089863, 
rb  .0000034 
Corrected,  .089866 


30  THE   ATOMIC   WEIGHTS. 


Now,  rejecting  nothing,  we  may  combine  all  the  series  into  a  general 
mean,  giving  the  weight  of  one  litre  of  hydrogen  as  follows  : 

First  series 089938,  ±  .000007 

Second  series 089970,  ±  .00001 1 

Preliminary  series,  second  method 089921,  ±  .0000271 

Third  series 089886,  zfc  .0000049 

Fourth     "    089880,  ±  .0000187 

Fifth        "    089866,  ±  .0000034 


General  mean 089897,  zfc  .0000025 

Rejecting  the  first  three 089872,  ±  .0000028 

This  last  mean  value  for  hydrogen  will  be  used  in  succeeding  chapters 
of  this  work  for  reducing  volumes  of  the  gas  to  weights.  Combining 
the  general  mean  of  all  with  the  value  found  for  the  weight  of  a  litre  of 
oxygen,  1.42896,  ±  .000028,  we  get  for  the  ratio  H  :  0, 

O  =  I5  8955,  ±  .0005 

If  we  take  only  the  second  mean  for  H,  excluding  the  first  three  series, 

we  have — 

O  =  15.9001,  ±  .0005 

This  value  is  undoubtedly  nearest  the  truth,  and  is  preferable  to  all 
other  determinations  of  this  ratio.  Its  probable  error,  however,  is  given 
too  low ;  for  some  of  the  oxygen  weighings  involved  reductions  for  tem- 
perature and  pressure.  These  reductions  involve,  again,  the  coefficient  of 
expansion  of  the  gas,  and  its  probable  error  should  be  included.  Since, 
however,  that  factor  has  been  disregarded  elsewhere,  it  would  be  an  over- 
refinement  of  calculation  to  include  it  here. 

In  a  memoir  of  this  kind  it  is  impossible  to  do  full  justice  to  so  elab- 
orate an  investigation  as  that  of  Morley.  The  details  are  so  numerous, 
the  corrections  so  thorough,  the  methods  for  overcoming  difficulties  so 
ingenious,  that  many  pages  would  be  needed  in  order  to  present  any- 
thing like  a  satisfactory  abstract.  Hardly  more  than  the  actual  results 
can  be  cited  here;  for  all  else  the  original  memoir  must  be  consulted. 

Still  more  recently,  by  a  novel  method,  J.  Thomsen  has  measured  the 
two  densities  in  question.*  In  his  gravimetric  research,  already  cited, 
he  ascertained  the  weights  of  hydrogen  and  of  oxygen  equivalent  to  a 
unit  weight  of  aluminum.  In  his  later  paper  he  describes  a  method  of 
measuring  the  corresponding  volumes  of  both  gases  during  the  same 
reactions.  Then,  having  already  the  weights  of  the  gases,  the  volume- 
weight  ratio,  or  density,  is  in  each  case  easily  computable.  From  1.0171 
to  2.3932  grammes  of  aluminum  were  used  in  each  experiment.  Omit- 
ting details,  the  volume  of  hydrogen  in  litres,  equivalent  to  one  gramme 
of  the  metal,  is  as  follows : 

*Zeitschr.  Anorg.  Chern.,  12,  4.     1896. 


OXYGEN.  31 

.24297 

•243Q3 
.24286 
.24271 
.24283 
.24260 

•243*4 
.24294 

Mean,  1.24289,  ±  .00004 

The  weight  of  hydrogen  evolved  from  one  gramme  of  aluminum  was 
found  in  Thomsen's  gravimetric  research  to  be  0.11190,  zb  .000015. 
Hence  the  weight  of  one  litre  at  0°,  760  mm.,  and  10.6  meters  above  sea 
level  at  Copenhagen  is  : 

.090032,  ±  .000012; 

or  at  sea  level  in  latitude  45°, 

.089947,  dh  .000012  gramme. 

The  data  for  oxygen  are  given  in  somewhat  different  form,  namely, 
for  the  volume  of  one  gramme  of  the  gas  at  0°,  760,  and  at  Copenhagen. 
The  values  are.  in  litres  : 

.69902 

.69923 

.69912 

.69917 

.69903 

.69900 

.69901 

.69921 

.69901 

.69922 


Mean,  .69910,  ±  .00002 
At  sea  level  in  latitude  45°,  .69976,  ±  .00002 

Hence  one  litre  weighs  1.42906,  ±  .00004  grammes. 

Dividing  this  by  the  weight  found  for  hydrogen,  0.089947,  ±  .000012 
we  have  for  the  ratio  H  :  0, 

15.8878,  ±  .0022. 


The  density  ratios,  H  :  0,  now  combine  as  follows  : 

Dumas  and  Boussingault,  corrected 15.9015,  d=  .031 

Regnault,  corrected 15.9105,  =b  .0044 

Rayleigh,  1888 15.884,    ±.0048 

"  1892 15.882,    ±.0023 

Cooke , 15.890,    ±  .0067 

Leduc i5-9°5»    ±  -OI54 

Morley,  including  all  the  data ., . .  15.8955,  ±  .0005 

Thomsen 15.8878,  ±  .0022 


General  mean 15.8948,  =h  .00048 


32  THE    ATOMIC    WEIGHTS. 

If  we  reject  all  of  Morley's  data  for  the  density  of  hydrogen  except  his 
third,  fourth,  and  fifth  series,  the  mean  becomes 

O  =  15.8991,  ±  .00048. 

In  either  case  Morley's  data  vastly  outweigh  all  others. 

If  oxygen  and  hydrogen  were  perfect  gases,  uniting  by  volume  to  form 
water  exactly  in  the  ratio  of  one  to  two,  then  the  density  of  the  first  in 
terms  of  the  second  would  also  express  its  atomic  weight.  But  in  fact, 
the  two  gases  vary  from  Boyle's  law  in  opposite  directions,  and  the  true 
composition  of  water  by  volume  diverges  from  the  theoretical  ratio  to  a 
measurable  extent.  Hence,  in  order  to  deduce  the  atomic  weight  of 
oxygen  from  its  density,  a  small  correction  must  be  applied  to  the  latter? 
dependent  upon  the  amount  of  this  divergence.  Until  recently,  our 
knowledge  of  the  volumetric  composition  of  water  rested  entirely  upon 
the  determinations  made  by  Humboldt  and  Gay-Lussac*  early  in  this 
century,  which  gave  a  ratio  between  H  and  0  of  a  little  less  than  2:1, 
but  their  data  need  no  farther  consideration  here. 

In  1887  Scott  t  published  his  first  series  of  experiments,  21  in  number, 
finding  as  the  most  probable  result  a  value  for  the  ratio  of  1.994  :  1.  In 
March,  1888, J  he  gave  four  more  determinations,  ranging  from  1.9962  to 
1.998:1;  and  later  in  the  same  year  §  another  four,  with  values  from 
1.995  to  2.001.  In  1893,  ||  however,  by  the  use  of  improved  apparatus, 
he  was  able  to  show  that  his  previous  work  was  vitiated  by  errors,  and  to 
give  a  series  of  measurements  of  far  greater  value.  Of  these,  twelve  were 
especially  good,  being  made  with  hydrogen  from  palladium  hydride, 
and  with  oxygen  from  silver  oxide.  In  mean  the  value  found  is 
2.00245,  ±  .00007,  with  a  range  from  2.0017  to  2.0030. 

In  1891  an  elaborate  paper  by  Morley^fl  appeared,  in  which  twenty 
concordant  determinations  of  the  volumetric  ratio  gave  a  mean  value  of 
2.00023,  ±  .000015.  These  measurements  were  made  in  eudiometer 
tubes,  and  were  afterwards  practically  discarded  by  the  author.  In  his 
later  and  larger  paper,**  however,  he  redetermined  the  ratio  from  the 
density  of  the  mixed  electrolytic  gases,  and  found  it  to  be,  after  applying 
all  corrections,  2.00274.  The  probable  error,  roughly  estimated,  is  .00005. 
Morley  also  reduces  Scott's  determinations,  which  were  made  at  the  tem- 
perature of  the  laboratory,  to  0°,  when  the  value  becomes  2.00285.  The 
mean  value  of  both  series  may  therefore  be  put  at  2.0028,  ±  .00004,  with 
sufficient  accuracy  for  present  purposes.  Leduc's  ft  single  determination, 

*  Journ.  de  Phys.,  60,  129. 

tProc.  Roy.  Soc.,  42,  396. 

I  Nature,  37,  439. 

g  British  Assoc.  Report,  1888,  631. 

I!  Proc.  Roy.  Soc.,  53,  130.    In  full  in  Philosophical  Transactions,  184,  543.     1893. 

^  Amer.  Journ.  Sci.  (3),  46,  220,  and  276. 

**  Already  cited  with  reference  to  syntheses  of  water. 

ft  Compt.  Rend.,  115,  311.     1892. 


OXYGEN.  33 

based  upon  the  density  of  the  mixed  gases  obtained  by  the  electrolysis 
of  water,  gave  2.0037 ;   but  Morley  shows  that  some  corrections  were 
neglected.     This  determination,  therefore,  may  be  left  out  of  account. 
Now,  including  all  data,  we  have  a  mean  value  for  the  density  ratio : 

(A.)  H  :O:  :  I  :  15.8948,  ±  .00048; 

or,  omitting  Morley's  rejected  series, 

(B.)  H  :O:  :  I  :  15.8991,  ±  .00048. 

Correcting  these  by  the  volume  ratio,  2.0028,  ±  .00004,  the  final  result 
for  the  atomic  weight  of  oxygen  as  determined  by  gaseous  densities 
becomes : 

From  A O  —  15.8726,  =b  .00058 

From  B O  =  15.8769,  ±  .00058 

Combining  these  with  the  result  obtained  from  the  syntheses  of  water, 
rejecting  nothing,  we  have — 

By  synthesis  of  water O  =  15.8837,  ±  .00026 

By  gaseous  densities O  =  15.8726,  ±  .00058 

General  mean O  =  15.8821,  ±  .00024 

If  we  reject  Reiser's  Work  under  the  first  heading,  and  omit  Morley's 
defective  hydrogen  series  under  the  second,  we  get — 

By  synthesis  of  water   O  —  15.8796,  ±  .00027 

By  gaseous  densities O  =  15.8769,  d=  .00058 

General  mean O  =  15.8794,  ±  .00025 

Morley,  discussing  his  own  data,  gets  a  final  value  of  O  =  15.8790,  ± 
.00026,  a  result  sensibly  identical  with  the  second  of  the  means  given 
above.  These  results  cannot  be  far  from  the  truth ;  and  accordingly, 
rounding  off  the  last  decimals,  the  value 

0  =  15.879,  ±.0003, 
will  be  used  in  computation  throughout  this  work. 

NOTE. — A  useful  "  short  bibliography  "  upon  the  composition  of  water, 
by  T.  C.  Warrington,  may  be  found  in  the  Chemical  News,  vol.  73,  pp. 
137,  145,  156,  170,  and  184. 


34  THE    ATOMIC    WEIGHTS. 


SILVER,   POTASSIUM,    SODIUM,   CHLORINE,    BROMINE,   AND 

IODINE. 

The  atomic  weights  of  these  six  elements  depend  upon  each  other  to 
so  great  an  extent  that  they  can  hardly  be  considered  independently. 
Indeed,  chlorine,  potassium,  and  silver  have  always  been  mutually  de- 
termined. From  the  ratio  between  silver  and  chlorine,  the  ratio  between 
silver  and  potassium  chloride,  and  the  composition  of  potassium  chlo- 
rate, these  three  atomic  weights  were  first  accurately  fixed.  Similar 
ratios,  more  recently  worked  out  by  Stas  and  others,  have  rendered  it 
desirable  to  include  bromine,  iodine,  and  sodium  in  the  same  general 
discussion. 

Several  methods  of  determination  will  be  left  altogether  out  of  account. 
For  example,  in  1842  Marignac*  sought  to  fix  the  atomic  weight  of 
chlorine  by  estimating  the  quantity  of  water  formed  when  hydrochloric 
acid  gas  is  passed  over  heated  oxide  of  copper.  His  results  were  wholly 
inaccurate,  and  need  no  further  mention  here.  A  little  later  Laurent  f 
redetermined  the  same  constant  from  the  analysis  of  a  chlorinated  de- 
rivative of  naphthalene.  This  method  did  not  admit  of  extreme  accu- 
racy, and  it  presupposed  a  knowledge,  of  the  atomic  weight  of  carbon  ; 
hence  it  may  be  properly  disregarded.  Maumene's  J  analyses  of  the 
oxalate  and  acetate  of  silver  gave  good  results  for  the  atomic  weight  of 
that  metal;  but  they  also  depend  for  their  value  upon  our  knowledge  of 
carbon,  and  will,  therefore,  be  discussed  farther  on  with  reference  to  that 
element.  Hardin's  §  work  also,  relating  to  the  nitrate,  acetate,  and 
benzoate  of  silver,  will  be  found  in  the  chapters  upon  nitrogen  and 
carbon. 

Let  us  now  consider  the  ratios  upon  which  we  must  rely  for  ascertain- 
ing the  atomic  weights  of  the  six  elements  in  question.  After  we  have 
properly  arranged  our  data  we  may  then  discuss  their  meaning.  First 
in  order  we  may  conveniently  take  up  the  percentage  of  potassium  chlo- 
ride obtainable  from  the  chlorate. 

The  first  reliable  series  of  experiments  to  determine  this  percentage 
was  made  by  Berzelius.  ||  All  the  earlier  estimations  were  vitiated  by 
the  fact  that  when  potassium  chlorate  is  ignited  under  ordinary  circum- 
stances a  little  solid  material  is  mechanically  carried  away  with  the 
oxygen  gas.  Minute  portions  of  the  substance  may  even  be  actually 
volatilized.  These  sources  of  loss  were  avoided  by  Berzelius,  who  de- 
vised means  for  collecting  and  weighing  this  trace  of  potassium  chloride. 

*Compt.  Rend.,  14,  570.     Also,  Journ.  f.  Prakt.  Chetn.,  26,  304. 
tConipt.  Rend.,  14,  456.    Journ.  f.  Prakt.  Chem.,  26,  307. 
t  Ann.  d.  Chim   et  d.  Phys.  (3),  18,  41.     1846. 
g Journ.  Arner.  Chem.  Soc.  18,  990.     1896. 
j|  Poggend.  Annalen,  8,  i.     1826. 


SILVER,    POTASSIUM,    ETC.  35 

All  the  successors  of  Berzelius  in  this  work  have  benefited  by  his  exam- 
ple, although  for  the  methods  by  which  loss  has  been  prevented  we  must 
refer  to  the  original  papers  of  the  several  investigators.  In  short,  then, 
Berzelius  ignited  potassium  chlorate,  and  determined  the  percentage  of 
chloride  which  remained.  Four  experiments  gave  the  following  results  : 

60.854 
60.850 
60.850 
60.851 

Mean,  60.851,  ±  .0006 

The  next  series  was  made  by  Penny,*  in  England,  who  worked  after 
a  somewhat  different  method.  He  treated  potassium  chlorate  with 
strong  hydrochloric  acid  in  a  weighed  flask,  evaporated  to  dryness  over 
a  sand  bath,  and  then  found  the  weight  of  the  chloride  thus  obtained. 
His  results  are  as  follows,  in  six  trials : 

60.825 
60.822 
60.815 
60.820 
60.823 
60.830 


Mean,  60.8225,  ±  .0014 

In  1842  Pelouze  f  made  three  estimations  by  the  ignition  of  the  chlo- 
rate, with  these  results : 

60.843 
60.857 
60.830 

Mean,  60.843,  ±  -°°53 

Marignac,  in  1842, J  worked  with  several  different  recrystallizations  of 
the  commercial  chlorate.  He  ignited  the  salt,  with  the  usual  precau- 
tions for  collecting  the  material  carried  off  mechanically,  and  also  exam- 
ined the  gas  which  was  evolved.  He  found  that  the  oxygen  from  50 
grammes  of  chlorate  contained  chlorine  enough  to  form  .003  gramme  of 
silver  chloride.  Here  are  the  percentages  found  by  Marignac : 

In  chlorate  once  crystallized 60.845 

In  chlorate  once  crystallized 60.835 

In  chlorate  twice  crystallized 60.833 

In  chlorate  twice  crystallized 60.844 

In  chlorate  three  times  crystallized 60.839 

In  chlorate  four  times  crystallized 60.839 

Mean,  60.8392,  ±  .0013 


*  Phil.  Transactions,  1839,  p.  20. 

f  Compt.  Rend.,  15,  959. 

I  Ann.  d.  Chera.  u.  Pharm.,  44,  18. 


36  THE    ATOMIC    WEIGHTS. 

In  the  same  paper  Marignac  describes  a  similar  series  of  experiments 
made  upon  potassium  perchlorate,  KC104.  In  three  experiments  it  was 
found  that  the  salt  was  not  quite  free  from  chlorate,  and  in  three  more 
it  contained  traces  of  iron.  A  single  determination  upon  very  pure 
material  gave  46.187  per  cent,  of  oxygen  and  53.813  of  residue. 

In  1845  two  series  of  experiments  were  published  by  Gerhardt.  *  The 
first,  made  in  the  usual  way,  gave  these  results : 

60.871 
60.881 
60.875 


Mean,  60.8757,  ±  .0020 

In  the  second  series  the  oxygen  was  passed  through  a  weighed  tube 
containing  moist  cotton,  and  another  filled  with  pumice  stone  and  sul- 
phuric acid.  Particles  were  thus  collected  which  in  the  earlier  series 
escaped.  From  these  experiments  we  get — 

60.947 
60.947 
60.952 


Mean,  60.9487,  ±  .0011 

These  last  results  were  afterwards  sharply  criticised  by  Marignac,f 
and  their  value  seriously  questioned. 

The  next  series,  in  order  of  time,  is  due  to  Maumene.J  This  chemist 
supposed  that  particles  of  chlorate,  mechanically  carried  away,  might 
continue  to  exist  as  chlorate,  undecomposed  ;  and  hence  that  all  previous 
series  of  experiments  might  give  too  high  a  value  to  the  residual  chloride. 
In  his  determinations,  therefore,  the  ignition  tube,  after  expulsion  of  the 
oxygen,  was  uniformly  heated  in  all  its  parts.  Here  are  his  percentages 

of  residue : 

60.788 
60.790 
60.793 
60.791 
60.785 
60.795 
60.795 

Mean,  60.791,  ±  .0009 

The  question  which  most  naturally  arises  in  connection  with  these  re- 
sults is,  whether  portions  of  chloride  may  not  have  been  volatilized,  and 

css\    I  /^a"f 


so  lost 


*  Compt.  Rend.,  21,  1280. 

}  Supp.  Bibl.  Univ.  de  Geneve,  Vol.  I. 

I  Ann.  d.  Chim.  et  d.  Phys.  (3),  18,  71.     1846. 


SILVER,    POTASSIUM,    ETC.  37 

Closely  following  Maumene's  paper,  there  is  a  short  note  by  Faget,* 
giving  certain  mean  results.  According  to  this  chemist,  when  potassium 
chlorate  is  ignited  slowly,  we  get  60.847  per  cent,  of  residue.  When  the 
ignition  is  rapid,  we  get  60.942.  As  no  detailed  experiments  are  given, 
these  figures  can  have  110  part  in  our  discussion. 

Last  of  all  we  have  two  series  determined  by  Stas.f  In  the  first  series 
are  the  results  obtained  by  igniting  the  chlorate.  In  the  second  series 
the  chlorate  was  reduced  by  strong  hydrochloric  acid,  after  the  method 
followed  by  Penny : 

First  Series. 
60.8380 
60.8395 
60.8440 
60.8473 
60.8450 

Mean,  60.84276,  dr  .OOI2 

Second  Series. 
6o.8t;o 
60.853 
60.844 

Mean,  60.849,  ±  .0017 

In  these  experiments  every  conceivable  precaution  was  taken  to  avoid 
error  and  insure  accuracy.  All  weighings  were  reduced  to^  a  vacuum 
standard ;  from  70  to  142  grammes  of  chlorate  were  used  in  each  experi- 
ment; and  the  chlorine  carried  away  with  the  oxygen  in  the  first  series- 
was  absorbed  by  finely  divided  silver  and  estimated.  It  is  difficult  to 
see  how  any  error  could  have  occurred. 

Now,  to  combine  these  different  series  of  experiments. 

Berzelius,  mean  result 60. 85 1 ,    dr  .0006 

Penny,  "  60.8225,  dr  .0014 

Pelouze,  "  60.843,     ±.°053 

Marignac,  " 60.8392,  dr  .0013 

Gerhardt,  1st  "  60.8757,  dr  .0020 

"  2d  V 60.9487,  dr  .0011 

Maumene,  "  60.791,    dr  .0009 

.Stas,  1st  "  60.8428,  dr  .0012 

"      2d  "  60.849,    ±.0017 


General  mean    from  all  nine  series, 
representing  forty  experiments 60.846,     db  .00038 

This  value  is  exactly  that  which  Stas  deduced  from  both  of  his  own 
series  combined,  and  gives  great  emphasis  to  his  wonderfully  accurate 

*  Ann.  d.  Chim.  et  d.  Phys.  (3),  18,  80.     1846. 
f  See  Aronstein's  translation,  p.  24Q. 


38  THE    ATOMIC    WEIGHTS. 

work.     It  also  finely  illustrates  the  compensation  of  errors  which  occurs 
in  combining  the  figures  of  different  experimenters. 

Similar  analyses  of  silver  chlorate  have  been  made  by  Marignac  and 
by  Stas.  Marignac's  data  are  as  follows  :  *  The  third  column  gives  the 
percentage  of  0  in  AgC103 : 

24.5 10  grin.  AgClO3  gave  18.3616  AgCl.  25  103 

25.809  "  19-3345      "  25.086 

30.306  22.7072     "  25.074 

28.358  21.2453     "  25.082        . 

28.287  "  21.1833     "  25.113 

57.170  "  42.8366     "  25.072 


Mean,  25.088,  zfc  .0044 

Stas  f  found  the  following  percentages  in  two  experiments  only : 

25,081 
25.078 


Mean,  25.0795,  H=  .0010 

Combined  with  Marignac's  mean  this  gives  a  general  mean  of  25,080, 
±  .0010 ;  that  is,  Marignac's  series  practically  vanishes. 

For  the  direct  ratio  between  silver  and  chlorine  there  are  seven  avail- 
able series  of  experiments.  Here,  as  in  many  other  ratios,  the  first  reliable 
work  was  done  by  Berzelius.  J 

He  made  three  estimations,  using  each  time  twenty  grammes  of  pure 
silver.  This  was  dissolved  in  nitric  acid.  In  the  first  experiment  the 
silver  chloride  was  precipitated  and  collected  on  a  filter.  In  the  second 
and  third  experiments  the  solution  was  mixed  with  h}Tdrochloric  acid 
in  a  flask,  evaporated  to  dry  ness,  and  the  residue  then  fused  and  weighed 
without  transfer.  One  hundred  parts  of  silver  formed  of  chloride  : 

132.700 
132.780 
132.790 


Mean,  132.757,  ±  .019 

Turner's  work  §  closely  resembles  that  of  Berzelius.  Silver  was  dis- 
solved in  nitric  acid  and  precipitated  as  chloride.  In  experiments  one, 
two,  and  three  the  mixture  was  evaporated  and  the  residue  fused.  In 
experiment  four  the  chloride  was  collected  on  a  filter.  A  fifth  experi- 
ment was  made,  but  has  been  rejected  as  worthless. 

The  results  were  as  follows :  In  a  third  column  I  put  the  quantity  of 
AgCl  proportional  to  100  parts  of  Ag. 

*Bitjl.  Univ.  de  Gen6ve,  46,  356.     1843. 

f  Aronstein's  translation,  p.  214. 

I  Thomson's  Annals  of  Philosophy,  1820,  v.  15,  89. 

g  Phil.  Transactions,  1829,291. 


SILVER,    POTASSIUM,    ETC. 


39 


28.407  grains  Ag  gave  37.737 
41.917  "  55-678 

40.006  "  53.143 

30.922  "  41.070 


132.844 
132.829 
'32.837 
132.818 

Mean,  132.832,  ^  .0038 


The  same  general  method  of  dissolving  silver  in  nitric  acid,  precipi- 
tating, evaporating,  and  fusing  without  transfer  of  material  was  also 
adopted  by  Penny.  *  His  results  for  100  parts  of  silver  are  as  follows,  in 

parts  of  chloride : 

132.836 
132.840 
132.830 
132.840 
132.840 
132.830 
132.838 

Mean,  132.8363,  ±  .0012 

In  1842  Marignacf  found  that  100  parts  of  silver  formed  132.74  of 
chloride,  but  gave  no  available  details.  Later,  $  in  another  series  of  de- 
terminations, he  is  more  explicit,  and  gives  the  following  data.  The 
weighings  were  reduced  to  a  vacuum  standard : 


79.853  grm.  Ag  gave  106.080  AgCl. 

69.905  "  92.864     " 

64.905  "  86.210     " 

92.362  "  122.693     " 

99.653  "  132.383     " 


Ratio,  132.844 

132-843 
132.825 
132.839 
132.844 


Mean,  132.839,  ±  .0024 

The  above  series  all  represent  the  synthesis  of  silver  chloride.  Mau- 
mene  §  made  analyses  of  the  compound,  reducing  it  to  metal  in  a  current 
of  hydrogen.  His  experiments  make  100  parts  of  silver  equivalent  to 
chloride : 

132.734 

132-754 

132.724 

132.729 

132.741 


By  Dumas 


Mean,  132.7364,  =b  .0077 

we  have  the  following  estimations  : 

9.954  Ag  gave  13.227  AgCl.         Ratio,  132.882 


19.976 


26.542 


132.869 
Mean,  132.8755,  ±  .0044 


*Phil.  Transactions,  1839,  28. 

iAnn.  Chetn.  Pharm.,  44,  21. 

I  See  Berzelius'  I^ehrbuch,  sth  Ed.,  Vol.  3,  pp.  1192,  1193. 

J  Ann.  d.  Chim.  et  d.  Phys.  (3),  18,  49.     1846. 

||  Ann.  Chem.  Pharm.,  113,  21.     1860. 


40 


THE    ATOMIC    WEIGHTS. 


Finally,  there  are  seven  determinations  by  Stas,*  made  with  his  usual 
accuracy  and  with  every  precaution  against  error.  In  the  first,  second, 
and  third,  silver  was  heated  in  chlorine  gas,  and  the  synthesis  of  silver 
chloride  thus  effected  directly.  In  the  fourth  and  fifth  silver  was  dis- 
solved in  nitric  acid,  and  the  chloride  thrown  down  by  passing  hydro- 
chloric acid  gas  over  the  surface  of  the  solution.  The  whole  was  then 
evaporated  in  the  same  vessel,  and  the  chloride  fused,  first  in  an  atmos- 
phere of  hydrochloric  acid,  and  then  in  a  stream  of  air.  The  sixth  syn- 
thesis was  similar  to  these,  only  the  nitric  solution  was  precipitated  by 
hydrochloric  acid  in  slight  excess,  and  the  chloride  thrown  down  was 
washed  by  repeated  decantation.  All  the  decanted  liquids  were  after- 
wards evaporated  to  dryness,  and  the  trace  of  chloride  thus  recovered 
was  estimated  in  addition  to  the  main  mass.  The  latter  was  fused  in  an 
atmosphere  of  HC1.  The  seventh  experiment  was  like  the  sixth,  only 
ammonium  chloride  was  used  instead  of  hydrochloric  acid.  From  98.3 
to  399.7  grammes  of  silver  were  used  in  each  experiment,  the  operations 
were  performed  chiefly  in  the  dark,  and  all  weighings  were  reduced  to 
vacuum.  In  every  case  the  chloride  obtained  was  beautifully  white. 
The  following  are  the  results  in  chloride  for  100  of  silver: 

132.841 

132.843 
132.843 
132.849 
132.846 
132.848 
122.8417 


Mean,  132.8445,  ±  .0008 

We  may  now  combine  the  means  of  these  seven  series,  representing  in 
all  thirty-three  experiments.  One  hundred  parts  of  silver  are  equivalent 
to  chlorine,  as  follows : 

Berzelius 32-757,    ±  .0190 

Turner 32.832,    ±  .0038 

Penny 32.8363,  ±  .0012 

Marignac , 32.839,     =b  .0024 

Maumene ' 32.7364,  ±  .0077 

Dumas 32-8755,  =t  .0044 

Stas 32.8445,  dr  .0008 

General  mean 32.8418,  ±  .0006 

Here,  again,  we  have  a  fine  example  of  the  evident  compensation  of 
errors  among  different  series  of  experiments.  We  have  also  another 
tribute  to  the  accuracy  of  Stas,  since  this  general  mean  varies  from  the 
mean  of  his  results  only  within  the  limits  of  his  own  variations. 

*Aronstein's  translation,  p.  171. 


SILVER,    POTASSIUM,    ETC.  41 

The  ratio  between  silver  and  potassium  chloride,  or,  in  other  words, 
the  weight  of  silver  in  nitric  acid  solution  which  can  be  precipitated  by 
a  known  weight  of  KC1,  has  been  fixed  by  Marignac  and  by  Stas.  Ma- 
rignac,*  reducing  all  weighings  to  vacuum,  obtained  these  results.  In 
the  third  column  I  give  the  weight  of  KC1  proportional  to  100  parts 

ofAg: 

i                           4-723§  grm-  Ag  =   3.2626  KG.  69.067 

22.725  "  15.001  "  69.050 

21.759  "  I5-°28  "  69.066 

21.909  "  15.131  "  69.063 

22.032  "  15.216  "  69.063 

25.122  "  17.350  "  69.063 

Mean,  69.062,  ±0017 

The  work  of  Stas  falls  into  several  series,  widely  separated  in  point  of 
time.  His  earlier  experiments  f  upon  this  ratio  may  be  divided  into 
two  sets,  as  follows :  In  the  first  set  the  silver  was  slightly  impure,  but 
the  impurity  was  of  known  quantity,  and  corrections  could  therefore  be 
applied.  In  the  second  series  pure  silver  was  employed.  The  potassium 
chloride  was  from  several  different  sources,  and  in  every  case  was  puri- 
fied with  the  utmost  care.  From  10.3  to  32.4  grammes  of  silver  were 
taken  in  each  experiment,  and  the  weighings  were  reduced  to  vacuum. 
The  method  of  operation  was,  in  brief,  as  follows :  A  definite  weight  of 
potassium  chloride  was  taken,  and  the  exact  quantity  of  silver  necessary, 
according  to  Prout's  hypothesis,  to  balance  it  was  also  weighed  out.  The 
metal,  with  suitable  precautions,  was  dissolved  in  nitric  acid,  and  the 
solution  mixed  with,  that  of  the  chloride.  After  double  decomposition 
the  trifling  excess  of  silver  remaining  in  the  liquid  was  determined  by 
titration  with  a  normal  solution  of  potassium  chloride.  One  hundred 
parts  of  silver  required  the  following  of  KC1 : 

First  Series. 
69.105 
69.104 
69.103 
69.104 

69.  IO2 


Mean,  69.1036,  d=  .0003 

Second  Series. 
69.105 
69.099 
69.107 
69.103 
69. 103 
69.105 
69.104 


*See  Berzelius'  I^ehrbuch,  sth  Ed.,  Vol.  3,  pp.  1192-3. 
fAronstein's  translation,  pp.  250-257. 


42  THE    ATOMIC    WEIGHTS. 

69.099 

69.1034 

69.104 

69.103 

69.102 

69.104 

69.104 

69.105 

69.103 

69.101 

69.105 


Mean,  69.1033,  =b  .0003 

In  these  determinations  Stas  did  not  take  into  account  the  slight  solu- 
bility of  precipitated  silver  chloride  in  the  menstrua  employed  in  the 
experiments.  Accordingly,  in  1882*  he  published  a. new  series,  in  which 
by  two  methods  he  remeasured  the  ratio,  guarding  against  the  indicated 
error,  and  finding  the  following  values  : 

69.1198 
69.11965 
69.121 
69.123 

Mean,  69.1209,  ± .0003 

Corrected  for  a  minute  trace  of  silica  contained  in  the  potassium 
chloride,  this  mean  becomes 

69.11903,  ±. 0003. f 

Still  later,  in  order  to  establish  the  absolute  constancy  of  the  ratio  in 
question,  Stas  made  yet  another  series  of  determinations,^  in  which  he 
employed  potassium  chloride  prepared  from  four  different  sources. 
One  lot  of  silver  was  used  throughout.  The  values  obtained  were  as- 

follows : 

69.1227 
69.1236 
69.1234 
69.1244 
69.1235 
69.1228 
69.1222 
69.1211 
69.1219 
69.1249 
69.1238 
69.1225 
69.1211 

*  Memoires  Acad.  Roy.  de  Beige,  t.  43.     1882. 
fSee  Van  der  Plaats,  Ann.  Chim.  Phys.  (6),  7,  15. 
I  Oeuvres  Posthumes,  edited  by  W,  Spring. 


SILVER,    POTASSIUM,    ETC.  43 

A  series  was  also  begun  in  which  one  sample  of  potassium  chloride 
was  to  be  balanced  against  silver  from  various  sources,  but  only  one 
result  is  given,  namely,  69.1240.  This,  with  the  previous  series,  gives  a 
mean  of  69.1230,  ±  .0002. 

Five  series  of  determinations  are  now  at  hand  for  the  ratio  Ag  :  KC1. 
They  combine  as  follows  : 

Marignac 69.062,    ±  .0017 

Stas,  ist  series 69. 1036,  ±  .0003 

"     2d      " 69.1033,  ±  .0003 

"     3d      "       ...., 69. 1190,  rb  .0003 

"     4th     " 69.1230,  ±  .0002 


General  mean 69.1143,  d=  .00013 

The  difference  between  the  highest  and  the  lowest  of  Stas'  series  cor- 
responds to  a  difference  of  0.021  in  the  atomic  weight  of  potassium.  The 
rejection  of  the  earlier  work  might  be  quite  justifiable,  but  would  exert 
a  very  slight  influence  upon  our  final  result. 

The  quantity  of  silver  chloride  which  can  be  formed  from  a  known 
weight  of  potassium  chloride  has  also  been  determined  by  Berzelius, 
Marignac  and  Maumene.  Berzelius  *  found  that  100  parts  of  KC1  were 
equivalent  to  194.2  of  AgCl ;  a  value  which,  corrected  for  weighings  in 
air,  becomes  192.32.  This  experiment  will  not  be  included  in  our  dis- 
cussion. 

In  1842  Marignac  f  published  two  determinations,  with  these  results 
from  100  KC1 : 

192.33 
192-34 

Mean,  corrected  for  weighing  in  air,  192.26,  ±  .003 

In  1846  Marignac  I  published  another  set  of  results,  as  follows.     The 

weighings  were  reduced  to  vacuum,     The  usual  ratio  is  in  the  third 
column : 

17.034  grm.  KC1  gave  32.761  AgCl.  192.327 

I4-427                              27.749     "  192.341 

15.028              "              28.910     "  192.374 

15.131                              29.102     "  192.334 

15.216              "              29.271      "  192.370 


Mean,  192.349,  ±  .006 

Three  estimations  of  the  same  ratio  were  also  made  by  Maumene  §  as 
follows  : 

*Poggend.  Annal.,  8,  i.     1826. 

f  Ann.  Chem.  Pharm.,  44,  21,     1842. 

t  Berzelius'  I^ehrbuch,  sth  E}d.,  Vol.  3,  pp.  1192,  1193. 

§  Ann.  d.  Chim.  et  d.  Phys.  (3),  18,  41.     1846. 


44  THE    ATOMIC    WEIGHTS. 

10.700  grm.  KC1  gave  20.627  AffCl.  192.776 

10.5195  "  20.273      "  192.716 

8.587  "  16.556     "  192.803 

Mean,  192.765,  ±  .017 

The  three  series  of  ten  experiments  in  all  foot  up  thus: 

Marignac,  1842 192.260,  ±  .003 

1846 192.349,  ±  .006 

Maumene 192  765,  ±  .017 


General  mean 192.294,  ±  .0029 

These  figures  show  clearly  that  the  ratio  which  they  represent  is  not 
of  very  high  importance.  It  might  be  rejected  altogether  without  im- 
propriety, and  is  only  retained  for  the  sake  of  completeness.  It  will 
obviously  receive  but  little  weight  in  our  final  discussion. 


In  estimating  the  atomic  weight  of  bromine  the  earlier  experiments  of 
Balard,  Berzelius,  Liebig,  and  Lowig  may  all  be  rejected.  Their  results 
were  all  far  too  low,  probably  because  chlorine  was  present  as  an  im- 
purity in  the  materials  employed.  Wallace's  determinations,  based  upon 
the  analysis  of  arsenic  tribromide,  are  tolerably  good,  but  need  not  be 
considered  here.  In  the  present  state  of  our  knowledge,  Wallace's 
analyses  are  better  fitted  for  fixing  the  atomic  weight  of  arsenic,  and 
will,  therefore,  be  discussed  with  reference  to  that  element. 

The  ratios  with  which  we  now  have  to  deal  are  closely  similar  to  those 
involving  chlorine.  In  the  first  place,  there  are  the  analyses  of  silver 
bromate  by  Stas.*  In  two  careful  experiments  he  found  in  this  salt  the 
following  percentages  of  oxygen  : 

20.351 
20.347 


Mean,  20.349,  ±  .0014 

There  are  also  four  analyses  of  potassium  bromate  by  Marignac. f  The 
salt  was  heated,  and  the  percentage  loss  of  oxygen  determined.  The 
residual  bromide  was  feebly  alkaline.  We  cannot  place  much  reliance 
upon  this  series.  The  results  are  as  follows  : 

28.7016 
28.6496 
28.6050 
28.7460 


Mean,  2^.6755,  ±  .0207 


*Aronstein's  translation,  pp.  200-206. 

fSee  E.  Mulder's  Overzigt,  p.  117;  or  Berzelius'  Jahresbericht,  24,  72. 


SILVER,    POTASSIUM,    ETC.  45 

When  silver  bromide  is  heated  in  chlorine  gas,  silver  chloride  is  formed. 
In  1860  Dumas*  employed  this  method  for  estimating  the  atomic  weight 
of  bromine.  His  results  are  as  follows.  In  the  third  column  I  give  the 
weight  of  AgBr  equivalent  to  100  parts  of  AgCl : 

2.028  grm.  AgBr  gave  1.547  AgCl.  131.092 

4.237  "  3.235     "  i30-974 

5.769  4-403     "  131.024 

Mean,  131.030,  ±  .023 

This  series  is  evidently  of  but  little  value. 

The  two  ratios  upon  which,  in  connection  with  Stas'  analyses  of 
silver  bromate,  the  atomic  weight  of  bromine  chiefly  depends,  are  those 
which  connect  silver  with  the  latter  element  directly  and  silver  with 
potassium  bromide. 

Marignac,f  to  effect  the  synthesis  of  silver  bromide,  dissolved  the 
metal  in  nitric  acid,  precipitated  the  solution  with  potassium  bromide, 
washed,  dried,  fused,  and  weighed  the  product.  The  following  quanti- 
ties of  bromine  were  found  proportional  to  100  parts  of  silver : 


Mean,  reduced  to  a  vacuum  standard,  74.077,  dr  .003 

Much  more  elaborate  determinations  of  this  ratio  are  due  to  Stas.J 
In  one  experiment  a  known  weight  of  silver  was  converted  into  nitrate, 
and  precipitated  in  the  same  vessel  by  pure  hydrobromic  acid.  The 
resulting  bromide  was  washed  thoroughly,  dried,  and  weighed.  In  four 
other  estimations  the  silver  was  converted  into  sulphate.  Then  a  known 
quantity  of  pure  bromine,  as  nearly  as  possible  the  exact  amount  neces- 
sary to  precipitate  the  silver,  was  transformed  into  hydrobromic  acid. 
This  was  added  to  the  dilute  solution  of  the  sulphate,  and,  after  precip- 
itation was  complete,  the  minute  trace  of  an  excess  of  silver  in  the  clear 
supernatant  fluid  was  determined.  All  weighings  were  reduced  to  a 
vacuum.  From  these  experiments,  taking  both  series  as  one,  we  get 
the  following  quantities  of  bromine  corresponding  to  100  parts  of  silver: 

74.0830 

74.0790 

74.0795 
74.0805 
74.0830 


Mean,  74.081,     db  .0006 


*Ann.  Chem.  Phartn.,  113,  20. 

f  E.  Mulder's  Overzigt,  p.  116.     Berzelius'  Jahresbericht,  24,  7; 

I  Aronstein's  translation,  pp.  154-170. 


46  THE   ATOMIC   WEIGHTS. 

In  his  paper  on  the  atomic  weight  of  cadmium,*  Huntington  gives 
three  syntheses  and  three  analyses  of  silver  bromide.  The  data  are  as 
follows,  with  the  usual  ratio  given  in  the  last  column : 

1.4852  grm.  Ag  gave      2.5855  AgBr.  74.084 

1.4080  2.4510     "  74-077 

1.4449  "  2.5150     "  74.060 

4.1450  grm.  AgBr  gave  2.3817  Ag.  74-°35 

1.8172  "  1.0437     "  74-i" 

4.9601  2.8497     «  74.057 

Mean,  74.071,  ±  .0072 

Similar  synthetic  data  are  also  given  by  Richards,  incidentally  to  his 
work  on  copper.f  There  are  two  sets  of  three  experiments  each,  which 
can  here  be  treated  as  one  series,  thus : 

:.H235  grm.  Ag  gave  1.93630  AgBr.  74-°73 

2-74335  "  74-044 

3.77170  "  74.076 

"  1.68205  "  74.053 

•"  1.6789  "  74.069 

1.6779  "  74-074 


Mean,  74.065,  ±  .0035 

Another  set  of  data  by  Richards  appears  in  his  research  upon  the 
atomic  weight  of  barium ;  J  in  which  BaBr2  was  balanced  against  silver, 
and  the  AgBr  was  also  weighed.  Richards  gives  from  these  data  the 
percentage  of  Ag  in  AgBr,  which  figures  are  easily  restated  in  the  usual 
form  as  follows: 

Percentage.  Ratio, 

57.460  74.034 

57-455  74.049 

57-447  74  073 

57-445  74-074 

57.448  74-070 

57.442  74-089 

57.451  74.061 

57-455  74-049 

57-443  74.086 

57-445  74-074 

57-445  74-074 


Mean,  74.067,  rb  .0034 

The  same  ratio  can  also  be  computed  indirectly  from  Cooke's  experi- 
ments upon  SbBr3,  Huntington's   on  CdBr2,  Thorpe's   on   TiBr4,  and 


*  Proc.  Amer.  Acad.,  1881. 

fProc.  Amer.  Acad.,  25,  pp.  199,  210,  211.     1890. 

I  Proc.  Amer.  Acad.,  vol.  28.     1893. 


SILVER,    POTASSIUM,    ETC.  47 

Thorpe  and  Laurie's  on  gold.  The  values  so  obtained  all  confirm  the 
results  already  given,  varying  within  their  limits,  but  having  probable 
errors  so  high  that  their  use  would  not  affect  the  final  mean.  The  latter 
is  obtained  as  follows  : 

Marignac 74.077,  ±  .0030 

Stas 74.o8i,  ±  .0006 

Huntington 74-O7 1 ,  =b  .0072 

Richards,  1st  series 74.065,  ±  .0035 

"          2d     "       74.067,^.0034 


General  mean. ...    74.080,  ±  .00057 

In  this  case  again,  as  in  so  many  others,  Stas'  work  alone  appears  at 
the  end,  the  remaining  data  having  only  corroborative  value. 

The  ratio  between  silver  and  potassium  bromide  was  first  accurately 
determined  by  Marignac.*  I  give,  with  his  weighings,  the  quantity  of 
KBr  proportional  to  100  parts  of  Ag : 

2.131  grm.  Ag  =    2.351  KBr.  110.324 

2.559  "  2.823  "  110.316 

2.447  2.700  "  110.339 

3.025  "  3.336  "  110.283 

3-946  4.353  "  110.314 

11.569  "  12.763  "  110.321 

20.120           "  22.191  "  110.293 


Mean,  corrected  for  weighing  in  air,  110.343,  ±,  .005 


Stas,f  working  in  essentially  the  same  manner,  as  when  he  fixed  the 
ratio  between  potassium  chloride  and   silver,  obtained  the  following 

results : 

110.361 
110.360 
110.360 
110.342 
110.346 
110.338 
110.360 
110.336 
110.344 
110.332 
110.343 

110.357 
110.334 
"0.335 

Mean,  110.3463,  ±.0020 

Combining  this  with  Marignac's  mean  result,  110.343,  ±  .005,  we  get 
a  general  mean  of  110.3459,  ±  .0019. 

*Berzelius'  Jahresbericht,  24,  72. 

•f-  Aronstein's  translation,  pp.  334-347. 


48  THE   ATOMIC   WEIGHTS. 

The  ratios  upon  which  we  must  depend  for  the  atomic  weight  of 
iodine  are  exactly  parallel  to  those  used  for  the  determination  of  bromine. 

To  begin  with,  the  percentage  of  oxygen  in  potassium  iodate  has  been 
determined  by  Millon.*  In  three  experiments  he  found : 

22.46 
22.49 

22.47 


Mean,  22.473,  ±  .°°5 

Millon  also  estimated  the  oxygen  in  silver  iodate,  getting  the  follow- 
ing percentages : 

17.05 
17.03 
17.06 


Mean,  17.047,  ±  .005 

The  analysis  of  silver  iodate  has  also  been  performed  with  extreme 
care  by  Stas.f  From  76  to  157  grammes  were  used  in  each  experiment, 
the  weights  being  reduced  to  a  vacuum  standard.  As  the  salt  could  not 
be  prepared  in  an  absolutely  anhydrous  condition,  the  water  expelled  in 
each  analysis  was  accurately  estimated  and  the  necessary  corrections  ap- 
plied. In  two  of  the  experiments  the  iodate  was  decomposed  by  heat, 
and  the  oxygen  given  off  was  fixed  upon  a  weighed  quantity  of  copper 
heated  to  redness.  Thus  the  actual  weights,  both  of  the  oxygen  and  the 
residual  iodide,  were  obtained.  In  a  third  experiment  the  iodate  was 
reduced  to  iodide  by  a  solution  of  sulphurous  acid,  and  the  oxygen  was 
estimated  only  by  difference.  In  the  three  percentages  of  oxygen  given 
below,  the  result  of  this  analysis  conies  last.  The  figures  for  oxygen  are 
as  follows : 

16.976 

16.972 

16.9761 

Mean,  16.9747,  d=  .0009 

This,  combined  with  Millon's  series  above  cited,  gives  us  a  general 
mean  of  16.9771,  ±  .0009. 

The  ratio  between  silver  and  potassium  iodide  seems  to  have  been  de- 
termined only  by  Marignac.J  and  without  remarkable  accuracy.  In  five 
experiments  100  parts  of  silver  were  found  equivalent  to  potassium  iodide 
as  follows : 

*Ann.  Chim.  Phys.  (3),  9,  400.     1843. 
fAronstein's  translation,  pp.  170-200. 
I  Berzelius'  I^ehrbuch,  5th  ed.,  3,  1196. 


SILVER,    POTASSIUM,    ETC.  49 

1.616  grm.  Ag  =    2.483X1.  Ratio,  153.651 

2.503            "             3.846     "  "       153.665 

3.427                          5.268     "  "       153.720 

2.141                         3.290     "  "       153-667 

10.821                        16.642     "  "       153.794 

Mean,  153.6994,  d=  .0178 

The  synthesis  of  silver  iodide  has  been  effected  by  both  Marignac  and 
Stas.  Marignac,  in  the  paper  above  cited,  gives  these  weighings.  In  the 
last  column  I  add  the  ratio  between  iodine  and  100  parts  of  silver: 

15.000  grm.  Ag  gave  31.625  Agl.  117.500 

14-79°  "  32.I70     "  H7.5I2 

18.545  "  40.339     "  H7.5I9 


Mean,  corrected  for  weighing  in  air,  117.5335,  ±  .0036 

Stas*  in  his  experiments  worked  after  two  methods,  which  gave,  how- 
ever, results  concordant  with  each  other  and  with  those  of  Marignac. 

In  the  first  series  of  experiments  Stas  converted  a  known  weight  of 
silver  into  nitrate,  and  then  precipitated  with  pure  hydriodicacid.  The 
iodide  thus  thrown  down  was  washed,  dried,  and  weighed  without  trans- 
fer. By  this  method  100  parts  of  silver  were  found  to  require  of  iodine : 

117.529 
117-536 


Mean,  117.5325,  ±  .0024 

In  the  second  series  a  complete  synthesis  of  silver  iodide  from  known 
weights  of  iodine  and  metal  was  performed.  The  iodine  was  dissolved 
in  a  solution  of  ammonium  sulphite,  and  thus  converted  into  ammonium 
iodide.  The  silver  was  transformed  into  sulphate  and  the  two  solutions 
were  mixed.  When  the  precipitate  of  silver  iodide  was  completely  de- 
posited the  supernatant  liquid  was  titrated  for  the  trifling  excess  of  iodine 
which  it  always  contained.  As  the  two  elements  were  weighed  out  in  the 
ratio  of  127  to  108,  while  the  atomic  weight  of  iodine  is  probably  a  little 
under  127,  this  excess  is  easily  explained.  From  these  experiments  two 
sets  of  values  were  deduced  ;  one  from  the  weights  of  silver  and  iodine 
actually  employed,  the  other  from  the  quantity  of  iodide  of  silver  col- 
lected. From  the  first  set  we  have  of  iodine  for  100  parts  of  silver  : 

"7-5390 
117.5380 

117-  53'8 


117.5420 
117.5300 


Mean,  117.5373,  db  .0015 


:  Aronstein's  translation,  pp.  136,  152. 


50  THE   ATOMIC   WEIGHTS. 

From  the  weight  of  silver  iodide  actually  collected  we  get  as  follows. 
For  experiment  number  three  in  the  above  column  there  is  no  equivalent 

here: 

117.529 
117.531 
117-539 
117-538 
ii7-530 

Mean,  H7-5334,  d=  .0014 

Now,  combining  these  several  sets  of  results,  we  have  the  following 
general  mean : 

Marignac H7-5335,  ±  .°°36 

Stas,  ist  series ii7-5325,  ±  -OO24 

"    2d     "       "7-5373,  ±.ooi5 

"    3d     "       II7-5334,  =t  .0014 

General  mean "7-5345,  ±.0009 

One  other  comparatively  unimportant  iodine  ratio  remains  for  us  to 
notice.  Silver  iodide,  heated  in  a  stream  of  chlorine,  becomes  converted 
into  chloride ;  and  the  ratio  between  these  two  salts  has  been  thus  deter- 
mined by  Berzelius  and  by  Dumas. 

From  Berzelius  *  we  have  the  following  data.  In  the  third  column  I 
give  the  ratio  between  Agl  and  100  parts  of  AgCl : 

5.000  grm.  Agl  gave  3.062  AgCl.  163.292 

12.212  "  7-4755     "  163.360 

Mean,  163.326,  ±  .023 

Dumas' f  results  were  as  follows: 

3.520  grm.  Agl  gave  2.149  AgCl.  163. 793 

7.011  "  4.281     "  163.770 


Mean,  163.782,  ±  .008 

General  mean  from  the  combination  of  both  series,  163.733,  ±  .0076. 

For  sodium  there  are  but  four  ratios  of  any  value  for  present  purposes. 

The  early  work  of  Berzelius  we  may  disregard  entirely,  and  confine 
ourselves  to  the  consideration  of  the  results  obtained  by"  Penny,  Pelouze, 
Dumas,  and  Stas,  together  with  a  single  ratio  measured  incidentally  by 
Earn  say  and  Aston. 

The  percentage  of  oxygen  in  sodium  chlorate  has  been  determined 
only  by  PennyJ,  who  used  the  same  method  which  he  applied  to  the 
potassium  salt.  Four  experiments  gave  the  following  results  : 

*  Ann.  Chim.  Phys.  (2),  40,  430.  1829. 
t  Ann.  Chem.  Pharm.,  113,  28.  1860. 
J  Phil.  Transactions,  1839,  p.  25. 


SILVER,   POTASSIUM,    ETC.  51 


Mean,  45.0705,  d=  .0029. 


The  ratio  between  silver  and  sodium  chloride  has  been  fixed  by  Pe- 
louze,  Dumas,  and  Stas.  Pelouze  *  dissolved  a  weighed  quantity  of  silver 
in  nitric  acid,  and  then  titrated  with  sodium  chloride.  Equivalent  to 
100  parts  of  silver  he  found  of  chloride : 

54.158 
54.125 
54.139 

Mean,  54.141,  ±  .0063 

By  Dumas  f  we  have  seven  experiments,  with  results  as  follows.  The 
third  column  gives  the  ratio  between  100  of  silver  and  NaCl : 

2.0535  grm.  NaCl  =    3-788  grm.  Ag.  54-2H 

2.169  4.0095  "  54.097 

4-3554  8.0425  "  54.155 

6.509  12.0140  "  54.178 

6.413  11-8375  "  54.175 

2.1746  4.012  "  54.202 

5-  "3  "             9-434  "  54.187 

Mean,  54.172,  ±  .0096 

Stas,J  applying  the  method  used  in  establishing  the  similar  ratio  for 
potassium  chloride,  and  working  with  salt  from  six  different  sources, 
found  of  sodium  chloride  equivalent  to  100  parts  of  silver : 

54.2093 
54.2088 
54.2070 
54-2070 
54.2070 
54.2060 
54.2076 
54.2081 
54-2083 
54.2089 

Mean,  54.2078,  ±  .0002 

As  in  the  case  of  the  corresponding  ratio  for  potassium  chloride,  these 
data  needed  to  be  checked  by  others  which  took  into  account  the  solu- 

*Cotnpt.  Rend.,  20,  1047.     1845. 

t  Ann.  Chem.  Pharm..  113.  31.     1860. 

J  Aronstein's  translation,  p.  274. 


52  THE    ATOMIC    WEIGHTS. 

bility  of  silver  chloride.     Such  data  are  given  in  Stas'  paper  of  1882,* 
and  four  results  are  as  follows : 

54.2065 

54.20676 

54.2091 

54-2054 

Mean,  54.20694,  db  .00045 

Corrected  for  a  trace  of  silica  in  the  sodium  chloride,  this  mean  becomes 
54.2046,  it  .O0045.t  Combining  all  four  series,  we  have  for  the  NaCl 
equivalent  to  100  parts  of  Ag — 

Pelouze 54-  HI,    ±  .0063 

Dumas 54- 172,    ±.0096 

Stas,  early  series 54.2078,  ±  .0002 

Stas,  late       "     54.2046,^.00045 

General  mean 54.2071,  ±  .00018 

Here  the  work  of  Stas  is  of  such  superior  excellence  that  the  other  de- 
terminations might  be  completely  rejected  without  appreciably  affecting 
our  final  results. 

In  their  research  upon  the  atomic  weight  of  boron,  Ramsay  and  Aston  J 
converted  borax  into  sodium  chloride.  In  the  latter  the  chlorine  was 
afterwards  estimated  gravimetrically  by  weighing  as  silver  chloride  on  a 
Gooch  filter.  Hence  the  ratio,  AgCl :  NaCl :  :  100  :  x,  as  follows  : 

3.0761  grm.  NaCl  gave  7.5259  AgCl.  Ratio,  40.874 

2.7700                                6.7794     "  "       40.859 

2.8930               "                7.0804     "  "       40-859 

2.7360               "               6.6960     «  "       40.860 

1.9187               "               46931      "  "       40.863 


Mean,  40.867,  ±  .0033 

Finally,  for  the  ratios  between  silver  and  sodium  bromide  we  have  one 
set  of  measurements  by  Stas.§  The  bromide  was  prepared  by  saturating 
Na.2C03  with  HBr.  The  NaBr  proportional  to  100  parts  of  silver  was — 

95.4420 

95-4383 
95.4426 

95-4392 


Mean,  95.4405,  ±  .0007 

We  have  now  before  us  the  data  for  computing,  with  greater  or  less 
accuracy,  the  atomic  weights  of  the  six  elements  under  discussion.     In 

*M£moires  Acad.  Roy.  de  Beige.,  43.     1882. 

fSee  Van  der  Plaats,  Ann.  Chim.  Phys.  (6),  7,  16.     1886. 

%  Chem.  News,  66,  92.     1892. 

I  Memoires  Acad.  Roy.  Beige.,  43.     1882. 


SILVER,    POTASSIUM,    ETC.  53 

all  there  are  nineteen  ratios,  involving  about  two  hundred  and  fifty 
separate  experiments.  These  ratios  may  now  be  tabulated  and  num- 
bered for  reference,  it  being  understood  that  the  probable  error  in  each 
case  is  that  of  the  last  term  in  the  proportion. 

(i.)  Percentage  of  O  in  KC1O3. . ...    39.154,    ±  .00038 

(2.)  "  "          KBrO3 28.6755,^.0207 

(3-)  "  KIO3 22.473,    ±.0050 

(4.)  NaClO3 45.0705,  ±  .0029 

(5.)  AgClO3 25.080,    d=  .0010 

(6.)  "  "          AgBrOs 20.349,    ±.0014 

(7-)  "  "         AgI03 16.9771,  ±  .0009 

(8.)  Ag  :  NaCl  :  :  ioo  :  54.2071,  ±  .00018 

(9.)  Ag  :  NaBr  :  :  100  :  95.4405,  ±  .0007 

(10.)  Ag  :  KC1  :  :  100  :  69.1143,  ±  .00013 

(li.)  Ag  :  KHr  :  :  100  :  110.3459,  ±  .0019 

(12.)  Ag  :  KI  :  :  100  :  J53-6994,  ±.0178 

(!3-)  Ag  :  Cl  :  :  loo  :  32.8418,  ±  .0006 

(14.)  Ag  :  Br  :  :  100  :  74.080,  ±  .00057 

(IS.)  Ag  :  I  :  :  ioo  :  117.5345,  ±  .0009 

(l6.)  AgCl  :  NaCl  :  :  IOO  :  40.867,  ±  .0033 

(17.)  KC1  :  AgCl  :  :  ioo  :  192.294,  db  .0029 

(18.)  AgCl  :  AgBr  :  :  ioo  :  131.030,  ±  .023 

(19.)  AgCl  :  Agl  :  :  ioo  :  163.733,  ±  .0076 

Now,  from  ratios  1  to  7,  inclusive,  we  can  at  once,  by  applying  the 
known  atomic  weight  of  oxygen,  deduce  the  molecular  weights  of  seven 
haloid  salts.  Let  us  consider  the  first  calculation  somewhat  in  detail. 

Potassium  chlorate  yields  39.154  per  cent,  of  oxygen  and  60.846  per 
cent,  of  residual  chloride.  For  each  of  these  quantities  the  probable 
error  is  ±  .00038.  The  atomic  weight  of  oxygen  is  15.879,  dz  .0003,  so 
that  the  value  for  three  atoms  becomes  47.637,  ±  .0009.  We  have  now 
the  following  simple  proportion  : 

39.154  :  60.846  :  :  47-637  :  •*, 

whence  the  molecular  weight  of  potassium  chloride  becomes  =  74.029. 
The  probable  error  being  known  for  the  first,  second,  and  third  term 
of  this  proportion,  we  can  easily  find  that  of  the  fourth  term  by  the 
formula  given  in  our  introduction.  It  is  dz  .0073.  By  this  method  we 
obtain  the  following  series  of  values,  which  may  conveniently  be  num- 
bered consecutively  with  the  foregoing  ratios : 

(20)  KC1,  from  (i)  =    74.029,  ±  .0073 

(21)  KBr,  "  (2)  =  118.487,  ±  .0923 

(22)  KI,  "  (3)  =  164.337,  ±  .0382 

(23)  NaCl,  "  (4)  =    58.057,  ±  .0050 

(24)  AgCl,  "  (5)  =  142.303,  ±  .0066 

(25)  AgBr,  "  (6)  =  186.463,  ±  .0137 

(26)  Agl,  "  (7)  =.  232.959,  ±.0134 


54  THE    ATOMIC    WEIGHTS. 

With  the  help  of  these  molecular  weights,  we  are  now  able  to  com- 
pute seven  independent  values  for  the  atomic  weight  of  silver. 

First,      from  (10)  and  (20) Ag  —  107.1 1 1,  db  .0106 

Second,     "  (u)  "  (21) "  =  107.378,^.0837 

Third,       "  (12)  "  (22) "  =  106.921,^.0278 

Fourth,      "  (  8  )  "  (23) "  =  107. 102,  ±  .0092 

Fifth,         "  (13)  "  (24) "  =  107.122,  ±  .0050 

Sixth,        "  (14)  "  (25) "  =107.113,  dr. 0079 

Seventh,   "  (15)  "  (26) "  =  107.091,  dr  .0062 

General  mean Ag  =  107. 108,  dr  .0031 

It  is  noticeable  that  five  of  these  values  agree  very  well.  The  second 
and  third,  however,  diverge  widely  from  the  average,  but  in  opposite 
directions  ;  they  have,  moreover,  high  probable  errors,  and  consequently 
little  weight.  Of  these  two,  one  represents  little  and  the  other  none  of 
Stas'  work.  Their  trifling  influence  upon  our  final  results  becomes 
curiously  apparent  in  the  series  of  silver  values  given  a  little  further 
along. 

When  we  consider  closely,  in  all  of  its  bearings,  any  one  of  the  values 
just  given,  we  shall  see  that  for  certain  purposes  it  must  be  excluded 
from  our  general  mean.  For  example,  the  first  is  derived  partly  from 
the  ratio  between  silver  and  potassium  chloride.  From  this  ratio,  the 
atomic  weight  of  one  substance  being  known,  we  can  deduce  that  of  the 
other.  We  have  already  used  it  in  ascertaining  the  atomic  weight  of 
silver,  and  the  value  thus  obtained  is  included  in  our  general  mean. 
But  if  from  it  we  are  to  determine  the  molecular  weight  of  potassium 
chloride,  we  must  use  a  silver  value  derived  from  other  sources  only,  or 
we  should  be  assuming  a  part  of  our  result  in  advance.  In  other  words, 
we  must  now  use  a  general  mean  for  silver  from  which  this  ratio  with 
reference  to  silver  has  been  rejected.  Hence  the  following  series  of  silver 
values,  which  are  lettered  for  reference : 

A.  General  mean  from  all  eight 107.108,  dr  .0031 

B.  "  excluding  the  first 107.108,  dr  .0032 

C.  "  "  second 107.107,  ±  .0031 

D.  "  third 107.1  IO,  rfc  .0031 

E.  "  "  fourth 107. 109,  dr  .0033 

F.  "  "  fifth 107.099,  dr  .0039 

G.  "  sixth 107.106,  dr  .0034 

H.  "  seventh  ....  107.113,  dr  .0036 

We  are  now  in  a  position  to  determine  more  closely  the  molecular 
weights  of  the  haloid  salts  which  we  have  already  been  considering. 

For  silver  chloride,  still  employing  the  formula  for  the  probable  error 
of  the  last  term  of  a  proportion,  we  get  the  following  values : 


SILVER,    POTASSIUM,  ETC.  55 

From  (5) AgCl  —  142.303,  ±  .0066 

From  (13)  and  (F) "  =  142.276,  ±  .0052 

From  ( 1 6)     "    (23) "  ==  142.063,  ±  .0168 

From  (17)     "    (20) "  =  142.353,^.0156 

From  ( 1 8)     "    (25) "  =  142.306,  =b  .0271 

From  (19)     "    (26) "  =  142.278,  =b  .0105 


General  mean AgCl  =  142. 277,  ±  .0036 

The  third  of  these  values  is  certainly  too  low,  and  although  it  reduces 
the  atomic  weight  of  chlorine  by  only  0.01,  it  ought  to  be  rejected.  The 
general  mean  of  the  other  five  values  is  AgCl  =  142.287,  ±  .0037.  Sub- 
tracting from  this  the  atomic  weight  of  silver,  107.108,  ±  .0031,  we  have 
for  the  atomic  weight  of  chlorine — 

€1  =  35.179,  ±  .0048. 
For  silver  bromide  three  ratios  are  available: 

From  (6) AgBr  =  186.463,  dr  .0137 

From  (14)  and  (G) "     =  186.450,  ±  .0050 

From  ( 1 8)     "     (24) "     =  186.459,^.0339 

General  mean AgBr=  186.452,  ±  .0054 

Hence,  applying  the  atomic  weight  of  silver  as  before — 

Br  =  79.344,  d=  .0062. 

For  silver  iodide  we  have — 

From  (7) ' Agl  =  232.950,  rh  .0134 

From  (15)  and  (H) .     "    =  233.008,  ±  .0079 

From  (19)     "    (24) "    =^232.997,^.0153 

General  mean Agl  =  232.996,  rb  .0062 

Hence, 

1=  125.888,  rb  .0069. 

For  the  molecular  weight  of  sodium  chloride  three  values  appear,  as 
follows : 

From  (4) NaCl  =  58.057,  ±  .0050 

From  (8)  and  (E) "  =  58.061,  ±  .0018 

From  (16)  "    AgCl "     :=  58.148,  ±  .0049 

General  mean NaCl  =  58.069,  rh  .0016 

Rejecting  the  third  value,  which  corresponds  to  the  rejected  value  for 
AgCl  and  throws  out  ratio  (16)  entirely,  the  mean  becomes 

•  NaCl  =  58.060,  dz  .0017 

From  (9)  and  (A) NaBr  =  102.224,  ±  .0031 


56       ,  THE    ATOMIC    WEIGHTS. 

Deducting  from  these  molecular  weights  the  values  already  found  for 
Cl  and  Br,two  measurements  of  the  atomic  weight  of  sodium  are  obtained, 
thus: 

From  NaCl Na  =  22.881,  ±  .0051 

FromNaBr..  .    "   =  22.880,  ±  .01 12 


General  mean Na  =  22.881,  ±   0046 

The  rejection  of  ratio  (16)  in  connection  with  the  atomic  weights  of 
sodium  and  chlorine  is  fully  justified  by  the  fact  that  the  data  which  it 
represents  were  never  intended  for  use  in  such  computations.  They  were 
obtained  incidentally  in  connection  with  work  upon  boron,  and  their 
consideration  here  may  have  some  bearing  later  upon  the  discussion  of 
the  last-named  element. 

For  potassium,  the  ratios  available  give  molecular  weights  for  the 
chloride,  bromide,  and  iodide.  For  the  chloride, 

From  (i) KC1  =  74.029,  db  .0073 

From  ( 10)  and  (B) "    =  74.027,^.0022 

From  (17)    "    (24) "    =  74.003,  ±  .0049 

General  mean KC1  =  74.025,  d=  .0019 

For  the  bromide  we  have — 

From  (2) KBr  =  118.487,  ±  .0923 

From  (n )  and  (C) "    =  118.188,  ±  .0073 

General  mean -.  . .    KBr  =  118.200,  ±  .0073 

And  for  the  iodide — 

( 

From  (3) KI  =  164.337,  ±  .0382 

From  (12)  and  (D) "  =  164.627,  =!=  .0052 

General  mean KI  =  164.622,  ±  .0051 

Combining  these  values  with  those  found  for  chlorine,  bromine,  and 
iodine,  we  have  three  values  for  the  atomic  weight  of  potassium,  as  fol- 
lows : 

From  KC1 K  =  38.846,  ±  .0078 

From  KBr "=  38.856,  ±  .0096 

From  KI "  =38.734,  ±  .0086 


General  mean K  =  38.817,  ±  .0051 

To  sum  up,  the  six  atomic  weights,  under  discussion  may  be  tabulated 
as  follows,  both  for  the  standard  chosen,  and  with  O  =  16  as  the  base  of 
the  system : 


SILVER,    POTASSIUM,    ETC.  t       57 

H=i.  <9=i6. 

Ag ,    107.108,  ±  .0031  107.924 

K. 38.817,^.0051  39.112 

Na 22.881,  ±  .0046  23.048 

Cl 35.179,  ±.0048  35-447 

Br 79.344,^.0062  79-949 

I 125.888,^.0069  126.847 

It  must  be  remembered  that  tbese  values  represent  the  summing  up 
of  work  done  by  many  investigators.  Stas'  ratios,  taken  by  themselves, 
give  various  results,  according  to  the  method  of  combining  them.  This 
computation  has  been  made  by  Stas  himself,  with  his  older  determina- 
tions, and  more  recently  by  Ostwald,*  Van  der  Plaats,f  and  Thomsen,  J 
all  with  the  standard  of  0  —  16.  By  Van  der  Plaats  two  sets  of  results 
are  given  :  one  with  Stas'  ratios  assigned  equal  weight  (A),  and  the  other 
with  each  ratio  given  weight  inversely  proportional  to  the  square  of  its 
mean  error  (B).  The  results  of  these  several  computations  may  well  be 
tabulated  in  comparison  with  the  values  obtained  in  my  own  general 
discussion,  thus  : 

Clarke.  Stas.  Ostwald.  V.  der P.,  A.  V.derP.,B.  Thomsen. 

Ag 107.924  107.930  107.9376          107.9202           107.9244  107.9299 

39-H2  39-*37  39-I361             39-T4i4            39-HO3,  39-I5°7 

23.048  23.043  23.0575             23.0453             23.0443    '  23.0543 

d 35-447          35-457          35-4529  35-4516  35-4565  35-4494 

Br 79-949  79  952  79-96^8  79-94Q7  79-9548  79.95 10 

I 126.847         126.850         126.8640  126.8445  126.8494  126.8556 

The  agreement  between  the  new  values  and  the  others  is  highly  satis- 
factory, and  gives  a  strong  emphasis  to  the  magnificent  accuracy  of  Stas' 
determinations.  No  severer  test  could  be  applied  to  them. 

*Lehrbuch  der  allgemeinen  Chemie,  i,  41.     1885. 

tCompt.  Rend.,  116,  1362.     1893. 

t  Zeitsch.  Physikal.  Chem.,  13,  726.     1894. 


58  THE    ATOMIC    WEIGHTS. 


NITROGEN. 

The  atomic  weight  of  nitrogen  has  been  determined  from  the  density 
of  the  gas,  and  from  a  considerable  variety  of  purely  chemical  ratios. 

Upon  the  density  of  nitrogen  a  great  many  experiments  have  been 
made.  In  early  times  this  constant  was  determined  by  Biot  and  Arago, 
Thomson,  Dulong  and  Berzelius,  Lavoisier,  and  others.  But  all  of  these 
investigations  may  be  disregarded  as  of  insufficient  accuracy ;  and,  as 
in  the  case  of  oxygen,  we  need  consider  only  the  results  obtained  by 
Dumas  and  Boussingault,  by  Regnault,  and  by  recent  investigators. 

Taking  air  as  unity,  Dumas  and  Boussingault*  found  the  density  of 
nitrogen  to  be — 

.970 
.972 
•974 

Mean,  .972,  ±  .00078 

For  hydrogen,  as  was  seen  in  our  discussion  of  the  atomic  weight  of 
oxygen,  the  same  investigators  found  a  mean  of  .0693,  ±  .00013.  Upon 
combining  this  with  the  above  nitrogen  mean,  we  find  for  the  atomic 
weight  of  the  latter  element,  N  =  14.026,  ±  .0295. 

By  Regnault  f  much  closer  work  was  done.  He  found  the  density  of 
nitrogen  to  be  as  follows  : 

.97148 
.97H8 
•97154 
.97155 
.97108 
.97108 


Mean,  .97137,  d=  .000062 

For  hydrogen,  Regnault's  mean  value  is  .069263,  ±  .000019.  Hence, 
combining  as  before,  N  =  14.0244  ±  .0039. 

Both  of  the  preceding  values  are  affected  by  a  correction  for  the  dif- 
ference in  volume  between  the  weighing  globes  when  full  and  when 
empty.  This  correction,  in  the  case  of  Regnault's  data,  has  been  meas- 
ured by  Crafts,J  who  gives  .06949  for  the  density  of  H,  and  .97138  for  N. 
Corrected  ratio,  N  =  13.9787.  If  we  assume  the  same  proportional  cor- 
rection for  the  determination  by  Dumas  and  Boussingault,  that  becomes 
N  =  13.9771. 

*Compt.  Rend.,  12,  1005.  1841. 
f  Compt.  Rend.,  20,  975.  1845. 
I  Compt.  Rend.,  106,  1664. 


NITROGEN.  59 

Von  Jolly,*  working  with  electrolytic  oxygen  and  with  nitrogen  pre- 
pared by  passing  air  over  hot  copper,  but  not  with  hydrogen,  compared 
the  weights  of  equal  volumes  of  the  two  gases,  with  results  as  follows  : 

Oxygen.       •  Nitrogen. 

.442470  1.269609 

.442579  .269389 

.442489  .269307 

.442570  .269449 

•442571  .269515 

.442562  .269443 

.442478  .    .269478 

Mean,  1.442545,  ±  .000013  Mean,  1.269455,  ±.  000024 

The  ratio,  when  O  =  16,  is  N  =  14.0802,  ±  .0003.  Corrected  by  Ray- 
leigh,  the  ratio  between  the  weights  becomes  14.0805.  If  0  =  15.879, 
dz  .0003,  the  final  value  for  N,  deducible  from  Von  Jolly's  data,  is  N  = 
13.974,  ±  .0004. 

The  next  determination  in  order  of  time  is  Leduc's.f  He  made  nine 
measurements  of  the  density  of  nitrogen,  giving  a  mean  of  .97203,  with 
extremes  of  .9719  and  .9721;  but  he  neglects  to  cite  the  intermediate 
values.  Taking  the  three  figures  given  as  representative,  and  assuming 
a  fair  distribution  of  the  other  values  between  the  indicated  limits,  the 
probable  error  of  the  mean  is  not  far  from  0.00002.  For  hydrogen  he 
found  .06948,  ±  .00006745.  The  ratio  between  the  two  densities  gives 
N  =  13.9901,  ±.0138. 

Lord  Rayleigh,^  preparing  nitrogen  by  passing  air  over  hot  copper, 
and  weighing  in  a  standard  globe,  obtained  the  following  weights  : 

2.31035 
2.31026 
2.31024 
2.31012 
2.31027 


Mean,  2.31025,  ±  000025 

With  corrections  for  temperature,  shrinkage  of  the  globe  when  ex- 
hausted, etc.,  this  becomes  2.30883,  as  against  2.37512  for  the  same  volume 
of  air.  Hence  the  density  of  N  =  .97209,  ±  .00001.  His  former  work 
on  hydrogen  gives  .06960,  ±  .0000084,  for  the  density  of  that  gas.  The 
ratio  is  N  =  13.9678,  ±  .0017. 

The  foregoing  data,  however,  all  apply  to  nitrogen  derived  from  the 
atmosphere.  In  a  later  memoir  Rayleigh  §  found  that  nitrogen  from 

*  Poggend.  Annalen  (2),  6,  529-530.     1879. 
fCompt.  Rend.,  113,  186.     1891. 
j  Proc.  Roy.  Soc.,  53,  134.     1894. 
I  Chem.  News,  69,  231.     1894. 


60  THE    ATOMIC   WEIGHTS. 

chemical  sources,  such  as  oxides  of  nitrogen,  ammonium  nitrate,  etc., 
was  perceptibly  lighter ;  and  not  long  afterwards  the  discrepancy  was 
explained  by  the  astonishing  discovery  of  argon.  The  densities  given, 
therefore,  are  all  too  high,  and  unavailable  for  any  discussion  of  atomic 
weight.  As,  however,  the  reductions  had  been  completed  in  nearly  all  . 
their  details  before  the  existence  of  argon  was  announced,  they  may  be 
allowed  to  remain  here  as  part  of  the  record.  Summing  up,  the  ratios 
found  between  hydrogen  and  atmospheric  u  nitrogen  "  are  as  follows : 

Dumas  and  Boussingault,  corrected 1 3.977 

Regnault,  "         13-979 

Von  Jolly,  " ij-974 

Leduc,  "         13.990 

Rayleigh,  "         13.968 

Perhaps  at  some  future  time,  when  the  density  of  argon  is  accurately 
known  and  its  amount  in  the  atmosphere  has  been  precisely  determined, 
these  figures  may  be  so  corrected  as  to  be  useful  for  atomic  weight  calcu- 
lations. 

In  discussing  the  more  purely  chemical  ratios  for  establishing  the 
atomic  weight  of  nitrogen,  we  may  ignore,  for  the  present,  the  researches 
of  Berzelius  and  of  Anderson.  These  chemists  experimented  chiefly 
upon  lead  nitrate,  and  their  work  is  consequently  now  of  greater  value 
for  fixing  the  atomic  weight  of  lead.  Their  results  will  be  duly  consid- 
ered in  the  proper  connection  further  on. 

The  ratio  between  ammonium  chloride  and  silver  has  been  determined 
by  Pelouze,  by  Marignac,  and  by  Stas.  The  method  of  working  is  essen- 
tially that  adopted  in  the  similar  experiments  with  the  chlorides  of 
sodium  and  potassium. 

For  the  ammonium  chloride  equivalent  to  100  parts  of  silver,  Pelouze* 
found  : 

49-556 
49-5<7 

Mean,  49.5365,  ±  .013 

Marignac  f  obtained  the  following  results.  The  usual  ratio  for  100 
parts  of  silver  is  given  also  : 


8.063  grm- 

Ag  =  3.992  grm.  NH4C1. 

49.510 

9.402 

4-656           " 

49-521 

10.339 

"           5.120           " 

49-521 

12.497 

"           6.191           " 

49.540 

"•337 

"           5-6i7           " 

49.546 

11.307 

5-595 

49-483 

4.326 

2.143 

49.538 

Mean,  49.523, 

±  -0055 

*Compt.  Rend.,  20.  1047.     1845. 

t  Berzelius'  Lehrbuch,  sth  ed.,  vol.  3,  1184,  1185. 


NITROGEN.  61 

But  neither  of  these  series  can  for  a  moment  compare  with  that  of 
Stas.  *  He  used  from  12.5  to  80  grammes  of  silver  in  each  experiment^ 
reduced  his  weighings  to  a  vacuum  standard,  and  adopted  a  great  variety 
of  precautions  to  insure  accuracy.  He  found  for  every  100  parts  of  silver 
the  following  quantities  of  NH4C1 : 

V 

49.600 

49.599 

49-597 

49.598 

49-597 

49-593 

49-597 

49-5974 

49.602 

49-597 
49598 
49-592 


Mean,  49-5973,   ±  .0005 

In  this  work,  as  with  the  similar  ratios  for  potassium  and  sodium 
chloride,  the  solubility  of  silver  chloride  was  not  guarded  against  so  fully 
as  is  needful.  Accordingly  Stas  published  a  new  series  of  determina- 
tions in  1882,f  carefully  checked  in  this  particular,  with  the  subjoined 
values  for  the  ratio : 

49.60001 
49-59999 
49-599 
49.600 

49.597 
Mean,  49-S992,  ±  .00039 

Combining  all  four  series,  we  have — 

Pelouze 49-5365,  =b  .013 

Marignac 49-523>    ±  -OQ55 

Stas,  early  series 49'5973,  d=  .0005 

Stas,  later      "     49.5992,  ±  .00039 


General  mean 49-5983,  ±  .00031 

In  the  paper  last  cited  Stas  also  gives  a  similar  series  of  determinations 
for  the  ratio  Ag  :  NH4Br  :  :  100  :  x.  The  results  are  as  follows,  with  re- 
duction to  vacuum : 

*  Aronstein's  translation,  pp.  56-58. 
fMemoires  Acad.  Roy.  de  Beige.,  43.     1882. 


62  THE   ATOMIC    WEIGHTS, 

90.831 

90.831 

90.8297 

90.823 

90.8317 

90.8311 

90.832 


Mean,  90.8299,  ±  .0008 

The  quantity  of  silver  nitrate  which  can  be  formed  from  a  known 
weight  of  metallic  silver  has  been  determined  by  Penny,  by  Marignac, 
and  by  Stas.  Penny  *  dissolved  silver  in  nitric  acid  in  a  flask,  evapo- 
rated to  dryness  without  transfer,  and  weighed.  One  hundred  parts  of 
silver  thus  gave  of  nitrate : 

157.430 
157-437 
157-458 
157.440 

157.43° 

157-455 

Mean,  157.4417,  ±  .0033 

Marignac'sf  results  were  as  follows.  In  the  third  column  they  are 
reduced  to  the  common  standard  of  100  parts  of  silver : 

68.987  grm.  Ag  gave  108.608  grm.  AgNO3.  1 57. 433 

57.844             "              9I-°47  I57.40I 

66.436             "            104.592           "  157.433 

70.340                           110.718  157.404 

200.000             "            3*4.894           "  157.447 

Mean,  157.4236,  ±  .0061 

Stas,t  employing  from  77  to  405  grammes  of  silver  in  each  experiment, 
made  two  different  series  of  determinations  at  two  different  times.  The 
silver  was  dissolved  with  all  the  usual  precautions  against  loss  and 
against  impurity,  and  the  resulting  nitrate  was  weighed,  first  after  long 
drying  without  fusion,  just  below  its  melting  point ;  and  again,  fused. 
Between  the  fused  and  the  unfused  salt  there  was  in  every  case  a  slight 
difference  in  weight,  the  latter  giving  a  maximum  and  the  former  a 
minimum  value. 

In  Stas'  first  series  there  are  eight  experiments;  but  the  seventh  he 
himself  rejects  as  inexact.  The  values  obtained  for  the  nitrate  from  100 

*  Phil.  Trans.,  1839. 

fBerzelius'  I^ehrbuch,  sth  ed.,  3,  pp.  1184,  1185. 

t  Aronstein's  translation,  pp.  305  and  315. 


NITKOGEN.  63 

parts  of  silver  are  given  below  in  two  columns,  representing  the  two  con- 
ditions in  which  the  salt  was  weighed.  The  general  mean  given  at  the 
end  I  have  deduced  from  the  means  of  the  two  columns  considered 
separately : 

Unfused.  Fused. 

IS7-492  157.474 

157-510  157.481 

157-485  157-477 

157.476  i57-47i 

157.478  157-47° 

T57.47I  157.463 

157.488  157-469 


Mean,  157.4857  Mean,  157.472 

General  mean,  157.474,  ±  .0014 

In  the  later  series  there  are  but  two  experiments,  as  follows  : 

Unfused.  Fused. 

157.4964  I57-488 

157.4940  i57-48o 

Mean,  157.4952  Mean,  157.484 

General  mean,  157.486,  ±  .0003 

The  reverse  ratio,  namely,  the  amount  of  silver  obtainable  from  a 
weighed  quantity  of  nitrate,  has  been  determined  electrolytically  by 
Hardin.*  The  data  obtained,  however,  are  reducible  to  the  same  form 
as  in  the  preceding  series,  and  all  are  properly  combinable  together. 
Pure  silver  was  dissolved  in  pure  aqueous  nitric  acid,  and  the  crystal- 
line salt  thus  formed  was  dried,  fused,  and  used  for  the  determinations. 
The  silver  nitrate,  mixed  with  an  excess  of  pure  potassium  cyanide  solu- 
tion, was  electrolyzed  in  a  platinum  dish.  The  results  obtained,  reduced 
to  vacuum  weights,  were  as  follows  : 

.31202  AgNO3  gave  .19812  Ag.  Ratio,  157.490 


.47832 

.30370  " 

157.498 

.56742 

.36030  " 

"   157.485 

.57728 

.36655  " 

"   157.490 

.69409 

.44075  " 

"   157.479 

.86367 

.54843  " 

"   157.479 

.868u 

"     -SS^o  " 

"   157.466 

.93716 

.59508  » 

"   157.485 

1.06170 

.67412  " 

"   157.494 

i 

1.19849 

"     .76104  " 

J<   157-477 

Mean,  157.484,  ± 

.0020 

*  Journ.  Amer.  Chem.  Soc., 

18,995.  1896. 

64  THE    ATOMIC    WEIGHTS. 

Now,  to  combine  all  five  sets  of  results : 

Penny 157-4417,  ±  -°°33 

Marignac 1 57-4236,  ±  .0061 

Stas,  ist  series 157.4740,  ±  .0014 

Stas,  2d      " 157.4860,  =h  .0003 

Hardin 157.484,    ±.0020 

General  mean 157-479,    ±.0003 

For  the  direct  ratio  between  silver  nitrate  and  silver  chloride  there  are 
two  series  of  estimations.  A  weighed  quantity  of  nitrate  is  easily  con- 
verted into  chloride,  and  the  weight  of  the  latter  ascertained.  In  two 
experiments  Turner*  found  of  chloride  from  100  parts  of  nitrate : 

84-357 
84.389 


Mean,  84.373,  i.on 

Penny ,t  in  five  determinations,  found  the  following  percentages: 

84-370 
84.388 
84.377 
84.367 
84-370 


Mean,  84.3744,  d=  .0025 

The  general  mean  from  both  series  is  84.3743,  ±  .0025. 

The  ratio  directly  connecting  silver  nitrate  with  ammonium  chloride 
has  been  determined  only  by  Stas.  J  The  usual  method  of  working  was 
followed,  namely,  nearly  equivalent  quantities  of  the  two  salts  were 
weighed  out,  the  solutions  mixed,  and  the  slight  excess  of  one  estimated 
by  titration.  In  four  experiments  100  parts  of  silver  nitrate  were  found 
equivalent  to  chloride  of  ammonium,  as  follows: 

3L489 
3L490 
31-487 
31.486 


Mean,  31.488,  ±  .0006 

I 

The  similar  ratio  between  potassium  chloride  and  silver  nitrate-  has 

been  determined  by  both  Marignac  and  Stas. 

*Phil.  Trans.,  1833,  537. 
fPhil.  Trans.,  1839. 
jAronstein's  translation,  p.  309. 


NITROGEN.  65 

Marignac*  gives  the  following  weights.  I  add  the  quantity  of  KC1 
proportional  to  100  parts  of  AgN03 :  , 

1.849  grm.  KC1  —    4.218  grm.  AgNO3.  43.836 

2.473             "             5.640             "  43-848 

3-3I7                           7.565  43.847 

2.926             "             6.670             "  43.868 

6.191             "           14.110             "  43.877 

4.351             "             9.918             "  43-870 

Mean,  43.858,  ±  .0044 

Stas'  f  results  are  given  in  three  series,  representing  silver  nitrate  from 
three  different  sources.  In  the  third  series  the  nitrate  was  weighed  in 
vacuo,  while  for  the  other  series  this  correction  was  applied  in  the  usual 
way.  For  the  KC1  equivalent  to  100  parts  of  AgN03  Stas  found : 

First  Series. 
43-878 
43.875 
43-875 
43-874 

Mean,  43.8755,  =h  .0005. 

Second  Series. 

43-864 
43.869 
43-876 


Mean,  43.8697,  ±  .0023 

Third  Series. 

43-894 
43-878 
43.885 


Mean,  43.8857,  ±  .0031 
i 

Combining  all  four  series  we  have : 

Marignac 43.858,     ±  .0044 

Stas,  ist  series 43-8755,  rfc  .o°°5 

Stas,  2d     "     43.8697,  ±  .0023 

Stas,  3d     " 43-8857,  ±  .0031 


General  mean 43.8715,  =h  .0004 

There  have  also  been  determined  by  Penny,  by  Stas,  and  by  Hibbs  a 
series  of  ratios  connecting  the  alkaline  chlorides  and  chlorates  with  the 
corresponding  nitrates.  One  of  these,  relating  to  the  lithium  salts,  will 
be  studied  farther  on  with  reference  to  that  metal. 

*Berzelius'  L,e'urbuch,  sth  ed.,  3d  vol.,  1184,  1185. 
t  Aronstein's  translation,  p.  308. 


66  THE   ATOMIC    WEIGHTS. 

The  general  method  of  working  upon  these  ratios  is  due  to  Penny.  * 
Applied  to  the  ratio  between  the  chloride  and  nitrate  of  potassium,  it  is 
as  follows :  A  weighed  quantity  of  the  chloride  is  introduced  into  a  flask 
which  is  placed  upon  its  side  and  connected  with  a  receiver.  An  excess 
of  pure  nitric  acid  is  added,  and  the  transformation  is  gradually  brought 
about  by  the  aid  of  heat.  Then,  upon  evaporating  to  dryness  over  a 
sand  bath,  the  nitrate  is  brought  into  weighable  form.  The  liquid  in 
the  receiver  is  also  evaporated,  and  the  trace  of  solid  matter  which  had 
been  mechanically  carried  over  is  recovered  and  also  taken  into  account. 
In  another  series  of  experiments  the  nitrate  was  taken,  and  by  pure  hy- 
drochloric acid  converted  into  chloride,  the  process  being  the  same.  In 
the  following  columns  of  figures  I  have  reduced  both  series  to  one  stand- 
ard, namely,  so  as  to  express  the  number  of  parts  of  nitrate  correspond- 
ing to  100  of  chloride : 

First  Series.— KCl  treated  with 

!35-639 
I35-637 
135-640 
135.635 
135-630 
135.640 
135-630 


Mean,  135.636,  ±  .0011 

Second  Series.— KNO^  treated  with  HCl. 
135.628 

135-635 
135-630 
135-641 
135  630 
135.635 
135-630 

Mean,  135.633,  ±  .0011 

Stas'  f  results  are  as  follows : 

135.643 
135-638 
135.647 

135-649 
135.640 

1 35 -645 
135.655 

Mean,  135.6453,  ±  .0014 

*Phil.  Trans.,  1839. 

t  Aronstein's  translation,  p.  270. 


NITROGEN. 


67 


These  figures  by  Stas  represent  weighings  in  the  air.  Reduced  to  a 
vacuum  standard,  this  mean  becomes  135.6423. 

The  determinations  made  by  Hibbs*  differ  slightly  in  method  from 
those  of  Penny  and  Stas.  He  converted  the  nitrate  into  the  chloride  by 
heating  in  a  stream  of  gaseous  hydrochloric  acid.  His  results  were  as 
follows,  vacuum  weights  being  given  • 


Weight  KNOZ  Weight  KCl. 
.11090  .08177 

.14871  .10965 

.21067  .15533 

.23360  .17225 

.24284  .17903 


Now,  combining,  we  have  : 


Ratio. 

135-624 
135.622 
135.627 
135.620 
135.642 


Mean,  135.627,  =h  .0026 


Penny,  ist  series J35-636,    ±  .001 1 

Penny,  2d      "      i35-633>    ±.0011 

Stas I35.6423,  ±  .0014 

Hibbs 135.627,    ±.0026 


General  mean 135.636,    ±.0007 

By  the  same  general  process  Penny  f  determined  how  much  potassium 
nitrate  could  be  formed  from  100  parts  of  chlorate.     He  found  as  follows  : 

82.505 
82.497 
82.498 
82.500 


Mean,  82.500,  ±  .0012 


For  100  parts  of  sodium  chlorate  he  found  of  nitrate  : 

79.875 
79-882 
79.890 

Mean,  79.8823,  4=  .0029 


For  the  ratio  between  the  chloride  and  nitrate  of  sodium  Penny  made 
two  sets  of  estimations,  as  in  the  case  of  potassium  salts.  The  subjoined 
figures  give  the  amount  of  nitrate  equivalent  to  100  parts  of  chloride : 

*  Thesis  for  Doctor's  degree,  University  of  Pennsylvania,  1896.     Work  done  under  the  direction 
of  Professor  E.  F.  Smith. 
fPhil.  Trans.,  1839. 


68  THE   ATOMIC    WEIGHTS. 

First  Series.— NaCl  treated  with 

I45-4T5 
145.408 
145.420 

145.424 
145.410 
145.418 
145.420 

Mean,  145.4164,  ±  .0015 

Second  Series. — NaNOz  treated  with  HCL 

I45-4I9 
I45-391 
145.412 

145.415 
145-412 
145.412 

Mean,  145.410,  ±  .0026 

Stas*  gives  the  following  series : 

145-453 
145.468 

145-465 
145.469 

145-443 

Mean,  after  reducing  to  vacuum  standard,  145.4526,  ±  .0030 

Hibbs't  data,  obtained  by  the  method  employed  in  the  case  of  the 
potassium  compounds,  are  as  follows,  vacuum  weights  being  stated : 

Weight  NaNOy  Weight  NaCl.  Ratio. 

.01550  .01066  i45-4°3 

.20976  .14426  I45.404 

.26229  .18038  145. 410 

.66645  .45829  145.429 

.93718  .64456  H5-399 

Mean,  145.407,  ±  .0026 

Combining,  we  have  as  follows : 

Penny,  1st  series 145.4164,  ±  .0015 

Penny,  2d      "     145.410,    ±.0026 

Stas 145.4526,  ±  .0030 

Hibbs 145.407,    ±:  .0026 

General  mean 145.418,    ±  .0012 

*  Aronstein's  translation,  p.  278. 

t  Thesis,  University  of  Pennsylvania,  1896. 


NITROGEN.  69 

Julius  Thomsen,  *  for  the  purpose  of  fixing  indirectly  the  ratio  H  :  O, 
has  made  a  valuable  series  of  determinations  of  the  ratio  HC1:NH3, 
which  may  properly  be  used  toward  establishing  the  atomic  weight  of 
nitrogen.  First,  pure,  dry,  gaseous  hydrochloric  acid  is  passed  into  a 
weighed  absorption  apparatus  containing  pure  distilled  water.  After 
noting  the  increase  in  weight,  pure  ammonia  gas  is  passed  in  until  a  very 
slight  excess  is  present,  and  the  apparatus  is  weighed  again.  The  excess 
of  NH3,  which  is  always  minute,  is  measured  by  titration  with  standard 
hydrochloric  acid.  In  weighing,  the  apparatus  is  tared  by  one  of  similar 
form,  arid  containing  about  the  same  amount  of  water.  Three  series  of 
determinations  were  made,  differing  only  in  the  size  of  the  absorption 
apparatus ;  so  that  for  present  purposes  the  three  may  be  taken  as  one. 
Thomsen  considers  them  separately,  and  so  gives  greatest  weight  to  the  ex- 
periments involving  the  largest  masses  of  material.  I  give  his  weighings, 

TT/tj 

and  also,  as  computed  by  him,  the  ratio     ^T. 


First  series. . 


Second  series. 


HCl. 

Nt?» 

Ratio. 

5.1624 

2.4120 

2.1403 

39425 

1.8409 

2.1416 

4.6544 

2.1739 

2.1411 

3.9840 

1.8609 

2.1409 

5.3295 

2.4898 

2.1406 

4-2517 

1.9863 

2.1405 

4.8287 

2.2550 

2.1414 

6.4377 

3.0068 

2.1411 

4.1804 

1.9528 

2.1407 

5-°363 

2.3523 

2.1410 

4.6408 

2.1685 

2.1411 

11.8418 

5-5302 

2.14130 

14.3018 

6.6808 

2.14073 

12.1502 

5.6759 

2.14067 

H-5443 

5.3927 

2.14073 

12.3617 

5-7733 

2.14118 

19-3455 

9.0360 

2.14094 

19.4578 

9.0890 

2.14081 

Third  series.. 


Mean  of  all,  2.14093,  ±  .000053 
Reduced  to  vacuo,  2.1394 

From  the  sums  of  the  weights  Thomsen  finds  the  ratio  to  be  2.14087, 
or  2.13934  in  vacuo.  From  this,  using  Ostwald's  reductions  of  Stas'  data 
for  the  atomic  weights  of  N  and  Cl,  he  finds  the  atomic  weight  of  H  = 
0.99946,  when  O  ==  16. 

We  have  now,  apart  from  the  determinations  of  gaseous  density,  eleven 
ratios,  representing  one  hundred  and  sixty-four  experiments,  from  which 

*  Zeitsch.  Physikal.  Chem.,  13,  398.     1894. 


70  THE    ATOMIC    WEIGHTS. 

to  calculate  the  atomic  weight  of  nitrogen.     Let  us  first  collect  and  num- 
ber these  ratios : 

(i.)  Ag  :  AgNO3  :  :  ioo  :  157-479,  ±  .o°°3 

(2.)   AgNO3  :  AgCl  :  :  ioo  :  84-3743,  ±  -OO25 

(3.)  AgNO3  :  KC1  :  :  ioo  :  43-87i5>  ±  .0004 

(4.)   AgNO3  :  NH4C1  :  :  ioo  :  31.488,  ±  .0006 

(5.)  Ag  :  NH4C1  :  :  ioo  :  49.5983,  dr  .00031 

(6.)   Ag  :  NH4Br  :  :  ioo  :  90.8299,  ±  .0008 

(7.)   KC1  :  KNO3  :  :  ioo  :  135.636,  ±  .0007 

(8.)  KC1O3  :  KN03  :  :  ioo  :  82.500,  ±  .0012 

(9.)   NaCl  :  NaNO3  :  :  ioo  :  145  418,  ±  .001 1 
(10.)   NaClO3  :  NaNO3  :  :  ioo  :  79.8823,  ±  .0029 
(n.)  NH3  :  HC1  :  :  i.oo  :  2.1394,  d=  .000053 

From  these  ratios  we  are  now  able  to  deduce  the  molecular  weight  of 
ammonium  chloride,  ammonium  bromide,  and  three  nitrates.  For  these 
calculations  we  must  use  the  already  ascertained  atomic  weights  of  oxy- 
gen, silver,  chlorine,  bromine,  sodium  and  potassium,  and  the  molecular 
weights  of  sodium  chloride,  potassium  chloride,  and  silver  chloride.  The 
following  are  the  antecedent  values  to  be  employed  : 

Ag  =  107.108,  d=  .0031 
K  =  38.817,  =b  .0051 
Na  —  22.881,  ±  .0046 
Cl  =  35.179,  =b  .0048 
Br  =  79.344,  ±  .0062 
O3  =  47.637,  ±  -0009 
AgCl  —  142.287,  ±  .0037 
KC1  =  74.025,  ±  .0019 
NaCl  =  58.060,  ±  .0017 

Now,  from  ratio  number  five  we  get  the  molecular  weight  of  NH4C1  = 
53.124,  ±  .0016,  and  N  =  13.945,  ±  .0051. 

From  ratio  number  six,  NH4Br  =  97.286,  ±  .0029,  and  N  =  13.942, 
±  .0077. 

From  ratio  number  eleven,  NH3  =  16.911,  ±  .0048,  and  N  =  13.911, 
±  .0048. 

From  ratio  number  four,  which  involves  an  expression  of  the  type 
A :  B  :  :  C  +  x :  D  +  x,  an  independent  value  is  deducible,  N  =  13.935, 
±  .0073. 

For  the  molecular  weight  of  silver  nitrate  there  are  three  values, 
namely  : 

From  (i) AgNO3  ==  168.673,  ±  .0049 

From  (2) "      =  168.634,  ±  .0066 

From  (3)    "       =  168.731,  ±  .0046 

General  mean AgNO3  =  168.690,  ±  .0030 

Hence  N=  13.945,  ±.0044. 


NITROGEN.  71 

The  molecular  weight  of  potassium  nitrate  is  twice  calculable,  as 
follows : 

From  (7) KNO3  =  100.405,  ±  .0026 

From  (8) "      —  100.371,  ±  .0059 

General  mean. . KNO3  =  100.401,  ±  .0024 

Hence  N  =  13.947,  ±  .0057. 
And  for  sodium  nitrate  we  have  : 

From  (9) NaNO3  =  84.430,  ±  .0026 

From  (.10) "      =  84.433,  ±  .0053 

General  mean NaNO3  =  84.431,  ±  .0023 

Hence  N  =  13.913,  ±  .0052. 

There  are  now  seven  estimates  of  the  atomic  weight  of  nitrogen,  to  be 
combined  by  means  of  the  usual  formula. 

1.  From  NH4C1 N  =  13.945,  ±  .0051 

2.  "     NH4Br "  =  13.942,  =h  .0077 

3.  "    ratio  (4) "  =  13.935,  ±.0073 

4-        "       "     (n) "  =  13.911,  ±.0048 

5.  "    AgNO3 "... "  =  13.945,^.0044 

6.  "    KNO3 "  =  13.947,  ±  .0057 

7.  "    NaNO3 "  =  13.913,  ±  .0052 

General  mean N  =•  13.935,  ±  .0021 

If  oxygen  is  16,  this  becomes  14.041.  From  Stas'  data  alone,  Stas 
finds  14.044 ;  Ostwald,  14.0410  ;  Van  der  Plaats,  14.0421  (A),  and  14.0519 
(B) ;  and  Thomsen,  14.0396.  The  new  value,  representing  all  available 
data,  falls  between  these  limits  of  variation. 


72  THE   ATOMIC   WEIGHTS. 


CARBON. 

Although  there  is  a  large  mass  of  material  relating  to  the  atomic  weight 
of  carbon,  much  of  it  may  be  summarily  set  aside  as  having  no  value 
for  present  purposes.  The  density  of  carbon  dioxide,  which  has  been 
scrupulously  determined  by  many  investigators,*  leads  to  no  safe  esti- 
mate of  the  constant  under  consideration.  The  numerous  analyses  of 
hydrocarbons,  like  the  analyses  of  naphthalene  by  Mitscherlich,  Wosk- 
resensky,  Fownes,  and  Dumas,  give  results  scarcely  more  satisfactory. 
In  short,  all  the  work  done  upon  the  atomic  weight  of  carbon  before  the 
year  1840  may  be  safely  rejected  as  unsuited  to  the  present  requirements 
of  exact  science.  As  for  methods  of  estimation  we  need  consider  but 
four,  as  follows : 

First.  The  analysis  of  organic  salts  of  silver. 

Second.  The  determination  of  the  weight  of  carbon  dioxide  formed  by 
the  combustion  of  a  known  weight  of  carbon. 

Third.  The  method  of  Stas,  by  the  combustion  of  carbon  monoxide. 

Fourth.  From  the  density  of  carbon  monoxide. 

The  first  of  these  methods,  which  is  probably  the  least  accurate,  was 
employed  by  Liebig  and  Redtenbacher  f  in  1840.  They  worked  with 
the  acetate,  tartrate,  racemate,  and  malate  of  silver,  making  five  ignitions 
of  each  salt,  and  determining  the  percentage  of  metal.  From  one  to 
nine  grammes  of  material  were  used  in  each  experiment. 

In  the  acetate  the  following  percentages  of  silver  were  found : 

64.615 
64.624 
64.623 
64.614 
64.610 

Mean,  64.6172,  ±  .0018 

After  applying  corrections  for  weighing  in  air,  this  mean  becomes 
64.6065. 

In  the  tartrate  the  silver  came  out  as  follows  : 

59.297 
59-299 
59-287 
59-293 
59-293 


Mean,  59  2938,  ±  .0014 
Or,  reduced  to  a  vacuum,  59.2806 


*  Notably  by  Lavoisier,  Biot  and  Arago,  De  Sauss'ure,  Dulong  and  Berzelius,  Buff,  Von  Wrede, 
Regnault,  and  Marchand.     For  details,  Van  Geun's  monograph  may  be  consulted, 
f  Ann.  Chem.  Pharm.,  38,  137.     Mem.  Chem.  Soc.,  i,  9.     Phil.  Mag.  (3),  19,  210. 


CARBON.  73 

In  the  racemate  we  have : 

59.290 
59.292 
59-287 
59.283 
59.284 


Mean,  59.2872,  ±  .0012 
Or,  corrected,  59.2769 

And  from  the  malate : 

61.996 
61.972 
62.015 
62.059 
62.011 


Mean,  62.0106,  zb  .0096 
Or,  corrected,  62.0016 

Now,  applying  to  these  mean  results  the  atomic  weights  already  found 
for  oxygen  and  silver,  we  get  the  following  values  for  carbon : 

From  the  acetate C  =  1 1-959,  ±  .0021 

From  the  tartrate "  —  11.967,  ±  .0019 

From  the  racemate "  =  11.973,  =h  .0017 

From  the  malate "  =  11.972,  ±  .0098 

Now  these  results,  although  remarkably  concordant,  are  by  no  means 
unimpeachable.  They  involve  two  possible  sources  of  constant  error, 
namely,  impurity  of  material  and  the  volatility  of  the  silver.  These 
objections  have  both  been  raised  by  Stas,  who  found  that  the  silver  tar- 
trate, prepared  as  Liebig  and  Redtenbacher  prepared  it,  always  carried 
traces  of  the  nitrate,  and  that  he,  by  the  ignition  of  that  salt,  could  not 
get  results  at  all  agreeing  with  theirs.  In  the  case  of  the  acetate  a  similar 
impurity  would  lower  the  percentage  of  silver,  and  thus  both  sources  of 
error  would  reinforce  each  other  and  make  the  atomic  weight  of  carbon 
come  out  too  high.  With  the  three  other  salts  the  two  sources  of  error 
act  in  opposite  directions,  although  the  volatility  of  the  silver  is  probably 
far  greater  in  its  influence  than  the  impurity.  Even  if  we  had  no  other 
data  relating  to  the  atomic  weight  of  carbon,  it  would  be  clear  from  these 
facts  that  the  results  obtained  by  Liebig  and  Redtenbacher  must  be 
decidedly  in  excess  of  the  true  figure. 

Strecker,  *  however,  discussed  the  data  given  by  Liebig  and  Redten- 
bacher by  the  method  of  least  squares,  using  the  Berzeliaii  scale,  and 
assuming  H  =  12.51.     Thus  treated,  they  gave  C  =  75.415,  and  Ag  = 
1348.79  ;  or,  with  0  =16,  C  =  12.066  and  Ag  =  107.903.     These  values 

*Ann.  Chem.  Pharm.,  59,  280.     1846. 


74  THE    ATOMIC    WEIGHTS. 

of  course  would  change  somewhat  upon  adoption  of  the  modern  ratio 
between  0  and  H. 

Observations  upon  silver  acetate,  like  those  of  Liebig  and  Redtenbacher, 
were  also  made  by  Marignac.*  The  salt  was  prepared  by  dissolving 
silver  carbonate  in  acetic  acid,  and  repeatedly  recrystallizing.  Two  ex- 
periments gave  as  follows : 

3-3359  grm«  acetate  gave  2.1561  Ag.  64.633  per  cent. 

3.0527  "  J-9727  "  64.621       " 

Mean,  64.627,  ±  .0040 

Reduced  to  a  vacuum,  this  becomes  64.609. 

In  a  second  series,  conducted  with  special  precautions  to  avoid  me- 
chanical loss  by  spurting,  Marignac  found: 

24.717  grm.  acetate  gave  15.983  Ag.  64.665  per  cent. 

21.202  "  13.709   "  64.661        " 

31.734  "  20.521    "  64.666       " 


Mean,  64.664,  ±  .0010 
Or,  reduced  to  a  vacuum,  64.646 

Other  experiments,  comparable  with  the  preceding  series,  have  recently 
been  published  by  Hardin,  f  who  sought  to  redetermine  the  atomic 
weight  of  silver.  Silver  acetate  and  silver  benzoate,  carefully  purified, 
were  subjected  to  electrolysis  in  a  platinum  dish,  and  the  percentage  of 
silver  so  determined.  For  the  acetate,  using  vacuum  weights,  he  gives 
the  following  data,  the  percentage  column  being  added  by  myself: 

.32470  grm.  acetate  gave  .20987  Ag.  64.635  per  cent. 

.40566  "  .26223    "  64.643  " 

.52736  "  .34086    "  64.635 

.60300  "'  .38976    "  64.637  " 

.67235  »  .43455    «  64.631  " 

.72452  "  .46830    "'  64.636  " 

.78232  "  .50563    "  64.632  " 

.79804  "  .51590    "  64.646 

.92101  "  .59532    "  64.638  ". 

1.02495  "  .66250    "  64.637  " 

Mean,  64.637,  ±  .0011 
Combining  this  series  with  those  of  the  earlier  investigators  we  have : 

Liebig  and  Redtenbacher 64.6065,  ±  .0018 

Marignac,  1st  series 64.609,    ±  .0040 

Marignac,  2d      "     64.646,    ±  .0010 

Hardin 64.637,    ±  .001 1 


General  mean 64.636,    ±  .0007 


*Ann.  Chem.  Pharm.,  59,  287.     1846. 

t  Journ.  Amer.  Chem.  Soc.,  18,  990.     1896. 


CARBOX.  75 

With  silver  benzoate,  C7H5Ag02,  Karelin's  results  are  as  follows : 

.40858  grm.  benzoate  gave  .19255  Ag.  47. 127  per  cent. 

.46674       "        -21999  "  47.133   " 

.48419        "        .22815  "  47.120   " 

.62432  .29418  "  47.120   " 

.66496       "       .3!34Q  "  47-I3I   " 

.75853  -35745  "  47.i24   " 

.76918  .36247  "  47.124   " 

.81254       "       .38286  "  47.H9   " 

.95673       "       .45079  "  47."8   " 

1.00840       "       .47526  "  47-I3°   " 


Mean,  47.125,  ±  .0012 

A  different  method  of  dealing  with  organic  silver  salts  was  adopted 
by  Maumene,*  in  1846,  for  the  purpose  of  establishing  by  reference  to 
carbon  the  atomic  weight  of  silver.  We  will  simply  reverse  his  results 
and  apply  them  to  the  atomic  weight  of  carbon.  He  effected  the  com- 
bustion of  the  acetate  and  the  oxalate  of  silver,  and,  by  weighing  both 
the  residual  metal  and  the  carbon  dioxide  formed,  he  fixed  the  ratio 
between  these  two  substances.  In  the  case  of  the  acetate  his  weighings 
show  that  for  every  gramme  of  metallic  silver  the  weights  of  CO2  were 
produced  which  are  shown  in  the  third  column : 

8.083  grm.  Ag=  6.585  grm.  CO2.  -8147 

11.215  "  9-J35  "  -8136 

I4.351  "  H.6935  "  -8148 

9.030  7.358  "  .8148 

20.227  "  16.475  "  .8145 

Mean,  .81448 

The  oxalate  of  silver,  ignited  by  itself,  decomposes  too  violently  to 
give  good  results ;  and  for  this  reason  it  was  not  used  by  Liebig  and 
Redtenbacher.  Maumene,  however,  found  that  when  the  salt  was  mixed 
with  sand  the  combustion  could  be  tranquilly  effected.  The  oxalate 
employed,  however,  with  the  exception  of  the  sample  represented  in  the 
last  experiment  of  the  series,  contained  traces  of  nitrate,  so  that  these 
results  involve  slight  errors.  For  each  gramme  of  silver  the  appended 
weights  of  C02  were  obtained  : 

14,299  grm.  Ag.  =  5.835  grm.  CO2.  .4081 


17.754 

7.217 

•4059 

".550 

4.703        " 

.4072 

10.771 

4-387 

•4073 

8.674 

3-533 

•4073 

"•4355 

4.658 

•  4073 

Mean,  .40718 

*Ann.  Chim.  Phys.  (3),  18,  41.     1846. 


76  THE    ATOMIC   WEIGHTS. 

New*,  one  of  these  salts  being  formed  by  a  bivalent  and  the  other  by  a 
univalent  acid,  we  have  to  reduce  both  to  a  common  standard.  Doing 
this,  we  have  the  following  results  for  the  ratio  between  the  atomic 
weight  of  silver  and  the  molecular  weight  of  CO2;  if  Ag  =  1.00  : 

From  the  acetate CO2  =  .40724,  ±  .000076 

From  the  oxalate •.  .    "    —  .40718,  =b  .000185 

General  mean CO2  =  .40723,  ±  .000071 

Here  the  slight  error  due  to  the  impurity  of  the  oxalate  becomes  of 
such  trifling  weight  that  it  practically  vanishes. 

As  has  already  been  said,  the  volatility  of  silver  renders  all  the  fore- 
going results  more  or  less  uncertain.  Far  better  figures  are  furnished  by 
the  combustion  of  carbon  directly,  as  carried  out  by  Dumas  and  Stas  * 
in  1840  and  by  Erdmann  and  Marchandf  in  1841.  In  both  investiga- 
tions weighed  quantities  of  diamond,  of  natural  graphite,  and  of  artificial 
graphite  were  burned  in  oxygen,  and  the  amount  of  dioxide  produced 
was  estimated  by  the  usual  methods.  The  graphite  employed  was  puri- 
fied with  extreme  care  by  treatment  with  strong  nitric  acid  and  by  fusion 
with  caustic  alkali.  I  have  reduced  all  the  published  weighings  to  a 
common  standard,  so  as  to  show  in  the  third  column  the  amount  of 
oxygen  which  combines  with  a  unit  weight  (say  one  gramme)  of  carbon. 
Taking  Dumas  and  Stas'  results  first  in  order,  we  have  from  natural 
graphite : 

i.ooo  grm.  C  gave  3.671  grm.  CO2.  2.6710 

.998     "     3.660    "  2.6673 

.994     "     3-645    "  2.6670 

i. 216          4.461    "  2.6686 

1.471     "     5-395    "  2.6676 

Mean,  2.6683,  =t  -oo°5 

With  artificial  graphite : 

.992  grm.  C  gave  3.642  grin.  CO2.  2.6714 

.998  "  3.662          "  2.6682 

1. 660  "  6.085          "  2.6654 

1.465  "  5-365          "  2.6744 


Mean,  2.66985,  ±  .0013 

And  with  diamond : 

.708  grm.  C  gave  2.598  grm.  CO2.  2.6695 

.864  3.1675        "  2.6661 

1.219  4.465          "  2.6628 

1.232  "  4.519          "  2.6680 

1.375  "  5.041          "  2.6662 


Mean,  5.6665  ±  .0007 


*  Compt.  Rend.,  11,  991-1008.    Ann.  Chira.  Phys.  (3),  i,  i. 
f  Jour,  f  Prakt.  Chem.,  23,  159. 


CARBON.  7/ 

Erdmann  and  Marchand's  figures  for  natural  graphite  give  the  follow- 
ing results : 

J-5376  grm-  gave  5.6367  grm.  CO2.  2.6659 

1.6494    "    6.0384    "  2.6609 

I-4505    "    5.31575   "  2.6647 

In  one  experiment  1.8935  grm.  of  artificial  graphite  gave  6.9355  grm. 

CO2.  Ratio  for  0,  2.6628.  This,  combined  with  the  foregoing  series, 
gives  a  mean  of  2.6636,  ±  .0007. 

With  the  diamond  they  found : 

.8052  grm.  gave  2.9467  grm.  CO2.  2.6596 

1.0858  "  3-9875  "  2.6632 

1.3557  "  4.9659  "  2.6629 

1-6305  "  5-97945  "  2.6673 

.7500    "    2.7490    "  2.6653 


Mean,  2.6637,  ±  .0009 

In  more  recent  years  the  ratio  under  consideration  has  been  carefully 
redetermined  by  Roscoe,  by  Friedel,  and  by  Van  der  Plaats.  Roscoe* 
made  use  of  transparent  Cape  diamonds,  and  in  a  sixth  experiment  he 
burned  carbonado.  The  combustions  were  effected  in  a  platinum  boat, 
contained  in  a  tube  of  glazed  Berlin  porcelain ;  and  in  each  case  the  ash 
was  weighed  and  its  weight  deducted  from  that  of  the  diamond.  The 
results  were  as  follows,  with  the  ratios  stated  as  in  the  preceding  series : 

1.2820  grm.  C  gave  4.7006  CO2.  2.6666 

1.1254  "  4.1245  "  2.6649 

1.5287  "  5.6050  "  2.6665 

.7112  "  2.6070  "  2.6656 

1.3842  "  5.0765  "  2.6675 

.4091     "     J-4978  "  2.6612 


Mean,  2.6654,  ±  .0006 

Friedel's  work,f  also  upon  Cape  diamond,  was  in  all  essential  par- 
ticulars like  Roscoe's.  The  data,  after  deduction  of  ash,  were  as  follows  : 

.4705  grm.  C  gave  1.7208  CO2.  2.6628 

.8616  "  3.1577    "  2.6640 

Mean,  2.6634,  ±  .0004 

By  Van  der  Plaats  J  we  have  six  experiments,  numbers  one  to  three 
on  graphite,  numbers  four  and  five  on  sugar  charcoal,  and  number  six 
on  charcoal  made  from  purified  filter  paper.  Each  variety  of  carbon 
was  submitted  to  elaborate  processes  of  purification,  and  all  weights  were 

*Ann.  Chini.  Phys.  (5),  26,  136.    Zeit.  Anal.  Chem.,  22,  306.    1883.    Compt.  Rend.,  94,  1180.     1882. 
fBull.  Soc.  Chim.,  42,  100,     1884. 
%  Compt.  Rend.,  100,  52.     1885. 


78  THE    ATOMIC    WEIGHTS. 

reduced  to  vacuum  standards.     The  data,  with  ash  deducted,  are  sub- 
joined : 

1.  5.1217  grm-  c  gave  18.7780  CO2.  2.6664 

2.  9.0532  "          33-I93i     "  2.6664 

3.  13.0285  "  47.7661  "  2.6663 

4.  11.7352  "  43.0210  "  2.6660 

5.  19.1335  "  7o.i336  "  2.6655 

6.  4.4017  16.1-352  "  2.6657 

Mean,  2.6660,  =fc  .0001 

This  combines  with  the  previous  series  thus  : 

Dumas  and  Stas,  first  set 2.6683,  ±  .0005 

Dumas  and  Stas,  second  set 2.66985,  ± .0013 

Dumas  and  Stas,  third  set 2.6665,  ±.0007 

Erdmann  and  Marchand,  first  set 2.6636,  ±  .0007 

Erdmann  and  Marchand,  second  set 2.6637,  ±  .0009 

Roscoe 2.6654,  d=  .0006 

Friedel 2.6634,  ±  .0004 

Van  der  Plaats 2.6660,  ±  .0001 


General  mean 2.6659,    ±  .0001 

Another  very  exact  method  for  determining  the  atomic  weight  of  car- 
bon was  employed  by  Stas*  in  1849.  Carefully  purified  carbon  mo- 
noxide was  passed  over  a  known  weight  of  copper  oxide  at  a  red  heat, 
and  both  the  residual  metal  and  the  carbon  dioxide  formed  were  weighed. 
The  weighings  were  reduced  to  a  vacuum  standard,  and  in  each  experi- 
ment a  quantity  of  copper  oxide  was  taken  representing  from  eight  to 
twenty-four  grammes  of  oxygen.  The  method,  as  will  at  once  be  seen, 
is  in  all  essential  features  similar  to  that  usually  employed  for  determin- 
ing the  composition  of  water.  The  figures  in  the  third  column,  deduced 
from  the  weights  given  by  Stas,  represent  the  quantity  of  carbon  mo- 
noxide corresponding  to  one  gramme  of  oxygen  : 

9.265  grm.  O  =  25.483  CO2.  .75046 

8.327  "  22.900     "  .75010 

13.9438  "  38.351     "  .75040 

11.6124  "  3L935     "  .75oo8 

18.763  "  51.6055  "  .75039 

19.581  "  53-8465  "  -74994 

22.515  "  61.926    "  .75043 

24.360  "  67.003    "  -75°53 


Mean,  1.75029,  db  .00005 

For  the  density  of  carbon  monoxide  the  determinations  made  by 
Leducf  are  available.     The  globe  used  contained  2.9440  grm.  of  air. 

*Bull.  Acad.  Bruxelles,  1849  (*),  31. 
fCompt.  Rend.,  115,  1072.     1893. 


CARBON.  79 

Filled  with  CO,  it  held  the  following  weights,  which  give  the  accom- 
panying densities : 

Wt.  CO.  Density. 

2.8470  -96705 

2.8468  .96698 

2.8469  .96702 

Mean,  .96702,  ±  .000015 

Combining  this  density  with  Leduc's  determination  of  the  density  of 
hydrogen,  0.6948,  ±  .00006745,  it  gives  for  the  atomic  weight  of  carbon : 

.C  =^.11.957,  ±.0270. 

Leduc  himself  combines  the  data  with  the  density  of  oxygen,  taken  as 
1.10503,  and  finds  0  =  11.913.  In  either  case,  however,  the  probable 
error  of  the  result  is  so  high  that  it  can  carry  little  weight  in  the  final 
combination. 

For  carbon,  including  all  the  foregoing  series,  we  now  have  the  sub- 
joined ratios  : 

(i.)  Per  cent.  Ag  in  silver  acetate 64.636,    ±  .0007 

(2.)          "  "  tartrate....    59.2806,  =b  .0014 

(3.)         "  "  racemate..    59.2769,1^.0012 

(4.)         "  malate  ....   62.0016,  ±".0096 

(5.)          "  benzoate...   47.125,    HT  .0012 

(•6.)  Ag  :  CO2  :  :  i.oo  :  0.40723,  ±  .000071 
(7.)   C  :  O2  :  :  i.oo  :  2.6659,  ±  .0001 
(8.)  O  :  CO  :  :  i.oo  :  1.75029,  ±  .00005 
(9.)  Density  of  CO  (air  =  i),  0.96702,  d=  .000015 

Now,  computing  with  0  =  15.879,  ±  .0003,  and  Ag  =  107.108,  ±  .0031, 
we  get  nine  values  for  the  atomic  weight  of  carbon,  as  follows : 

From  (i) C=  11.921,  ±  .0012 

From  (2) "  —  11.967,  ±  .0019 

From  (3) "•=  11.973,  ±.0017- 

From  (4) "  =  11.972,  ±  .0098 

From  (5) ..."==  11.917,  ±  .0008 

From  (6) "  =  11.860,  ±  .0077 

From  (7) "  —  11.913,  ±  .0006 

From  (8) "  =  11.914,  ±  .0010 

From  (9) "  =  11.957,  db  .0270 

General  mean C  =  11.920,  ±  .0004 

If  0  =  16,  this  becomes  C  =  12.011. 


80  THE   ATOMIC   WEIGHTS. 


SULPHUR. 

The  atomic  weight  of  sulphur  has  been  determined  hy  means  of  four 
ratios  connecting  it  with  silver,  chlorine,  oxygen,  sodium  ancl  carbon. 
Other  ratios  have  also  been  considered,  but  they  are  hardly  applicable 
here.  The  earlier  results  of  Berzelius  wrere  wholly  inaccurate,  and  his 
later  experiments  upon  the  synthesis  of  lead  sulphate  will  be  used  in 
discussing  the  atomic  weight  of  lead.  Erdmann  and  Marchand  deter- 
mined the  amount  of  calcium  sulphate  which  could  be  formed  from  a 
known  weight  of  pure  Iceland  spar;  and  later  they  made  analyses  of 
cinnabar,  in  order  to  fix  the  value  of  sulphur  by  reference  to  calcium  and 
to  mercury.  Their  results  will  be  applied  in  this  discussion  toward  ascer- 
taining the  atomic  weights  of  the  metals  just  named. 

First  in  order  let  us  take  up  the  composition  of  silver  sulphide,  as 
directly  determined  by  Dumas,  Stas,  and  Cooke.  Dumas'*  experiments 
were  made  with  sulphur  which  had  been  thrice  distilled  and  twice  crys- 
tallized from  carbon  disulphide.  A  known  weight  of  silver  was  heated 
in  a  tube  in  the  vapor  of  the  sulphur,  the  excess  of  the  latter  was  distilled 
away  in  a  current  of  carbon  dioxide,  and  the  resulting  silver  sulphide 
was  weighed. 

I  subjoin  Dumas'  weighings,  and  also  the  quantity  of  Ag2S  proportional 
to  100  parts  of  Ag,  as  deduced  from  them : 

9-9393  grm-  Ag=  1.473    s-  Ratio,  114.820 

9.962                        1.4755  "  "      114.811 

30.637                       4.546    "  "      114.838 

30.936                       4.586    "  "      114.824 

30.720                       4.554    "  "      114.824 

Mean,  114.8234,  rb  .0029 

Dumas  used  from  ten  to  thirty  grammes  of  silver  in  each  experiment. 
Stas,  f  however,  in  his  woi&  employed  from  sixty  to  two  hundred  and 
fifty  grammes  at  a  time.  Three  of  Stas'  determinations  were  made  by 
Dumas'  method,  while  in  the  other  two  the  sulphur  was  replaced  by  pure 
sulphuretted  hydrogen.  In  all  cases  the  excess  of  sulphur  was  expelled 
by  carbon  dioxide,  purified  with  scrupulous  care.  Impurities  in  the 
dioxide  may  cause  serious  error.  The  five  results  come  out  as  follows 
for  100  parts  of  silver : 

114.854 

114.853 
114.854 
114.851 
114.849 

Mean,  114.8522,  ±  .00x37 

*Ann.  Chem.  Pharm.,  113,  24.     1860. 
t  Aronstein's  translation,  p.  179. 


SULPHUR.  81 

The  experiments  made  by  Professor  Cooke*  with  reference  to  this  ratio 
were  only  incidental  to  his  elaborate  researches  upon  the  atomic  weight 
of  antimony.  They  are  interesting,  however,  for  two  reasons  :  they  serve 
to  illustrate  the  volatility  of  silver,  and  they  represent,  not  syntheses, 
but  reductions  of  the  sulphide  by  hydrogen.  Cooke  gives  three  series  of 
results.  In  the  first  the  silver  sulphide  was  long  heated  to  full  redness 
in  a  current  of  hydrogen.  Highly  concordant  and  at  the  same  time 
plainly  erroneous  figures  were  obtained,  the  error  being  eventually  traced 
to  the  fact  that  some  of  the  reduced  silver,  although  not  heated  to  its 
melting  point,  was  actually  volatilized  and  lost.  The  second  series,  from 
reductions  at  low  redness,  are  decidedly  better.  In  the  third  series  the 
sulphide  was  fully  reduced  below  a  visible  red  heat.  Rejecting  the  first 
series,  we  have  from  Cooke's  figures  in  the  other  two  the  subjoined  quan- 
tities of  sulphide  corresponding  to  100  parts  of  silver : 

7.5411  grm.  Ag2S  lost  .9773  grm.  S.  Ratio,  114.889 

5.0364                             .6524       "  "       114.882 

2.5815                              -3345        "  "       114.886 

2.6130                             .3387       "  "       114.892 

2.5724                              .3334       "  "       114.891 

Mean,  114.888,  ±  .0012 

I-I357  Srm-  AS2$  lost  -1465  S.  Ratio,  114.810 

1.2936  .1670  "  "       114.823 

Mean,  114.8165,  db  .0044 

Now,  combining  all  four  series,  we  get  the  following  results : 

Dumas 1 14.8234,  ±  .0029 

Stas '.'-..  114.8522,^.0007 

Cooke's  2d 114.888,    ±.0012 

Cooke's  3d 1 14.8165,  d=  .0044 


General  mean 1 14.8581,  d=  .0006 

Here  again  we  encounter  a  curious  and  instructive  compensation  of 
errors,  and  another  evidence  of  the  accuracy  of  Stas. 

The  percentage  of  silver  in  silver  sulphate  has  been  determined  by 
Struve  and  by  Stas.  Struve  t  reduced  the  sulphate  by  heating  in  a  cur- 
rent of  hydrogen,  and  obtained  these  results  : 

5.1860  grm.  Ag?SO4  gave  3.5910  grm.  Ag.  69.244  per  cent. 

6.0543  4.1922         "  69.243 

8.6465  "  5.9858         "  69.228       " 

11.6460  8.0608         "  69.215        " 

9.1090  6.3045          "  69.212       " 

9.0669  "  62778         "  69.239       " 


Mean 


*  Proc.  Ainer.  Acad.  of  Arts  of  Sciences,  vol.  12.     1877. 
f  Ann.  Chem.  Pharm.,  80,  203.     1^51. 


82  THE   ATOMIC    WEIGHTS. 

Stas,*  working  by  essentially  the  same  method,  with  from  56  to  83 
grammes  of  sulphate  at  a  time,  found  these  percentages : 

69.200 
69.197 
69.204 
69.209 
69.207 
69.202 


Mean,  69.203,  ±  .0012 

Combining  this  mean  with  that  from  Struve's  series,  we  get  a  general 
mean  of  69.205,  ±  0011. 

The  third  sulphur  ratio  with  which  we  have  now  to  deal  is  one  of 
minor  importance.  When  silver  chloride  is  heated  in  a  current  of  sul- 
phuretted hydrogen  the  sulphide  is  formed.  This  reaction  was  applied 
by  Berzelius  f  to  determining  the  atomic  weight  of  sulphur.  He  gives 
the  results  of  four  experiments ;  but  the  fourth  varies  so  widely  from  the 
others  that  I  have  rejected  it.  I  have  reason  to  believe  that  the  varia- 
tion is  due,  not  to  error  in  experiment,  but  to  error  in  printing ;  never- 
theless, as  I  am  unable  to  track  out  the  cause  of  the  mistake,  I  must 
exclude  the  figures  involving  it  entirely  from  our  discussion. 

The  three  available  experiments,  however,  give  the  following  results : 
The  last  column  contains  the  ratio  of  silver  sulphide  to  100  parts  of 
chloride. 

6.6075  grm.  AgCl  gave  5.715  grm.  Ag.2S.  86.478 

9.2323  "  7-98325       "  86.471 

10.1775  "  8.80075       "  86.472 

Mean,  86.4737,  db  .0015 

We  have  also  a  single  determination  of  this  value  by  Svanberg  and 
Struve.J:  After  converting  the  chloride  into  sulphide  they  dissolved  the 
latter  in  nitric  acid.  A  trifling  residue  of  chloride,  which  had  been 
enclosed  in  sulphide,  and  so  protected  against  change,  was  left  undis- 
solved.  Hence  a  slight  constant  error  probably  affects  this  whole  ratio. 
The  experiment  of  Svanberg  and  Struve  gave  86.472  per  cent,  of  silver 
sulphide  derived  from  100  of  chloride.  If  we  assign  this  figure  equal 
weight  with  the  results  of  Berzelius,  and  combine,  we  get  a  general  mean 
of  86.4733,  ±  .0011. 

The  work  done  by  Richards  §  relative  to  the  atomic  weight  of  sulphur 
is  of  a  different  order  from  any  of  the  preceding  determinations.  Sodium 
carbonate  was  converted  into  sodium  sulphate,  fixing  the  ratio  Na2COs : 
NaaS04 :  :  100  :  x.  The  data  are  as  follows,  with  vacuum  weights  : 

*  Aronstein's  translation,  pp.  214-218. 

f  Berzelius'  Lehrbuch,  sth  ed.,  vol.  3,  p.  1187. 

t  Journ.  Prakt.  Chem.,  44,  320.     1848. 

I  Proc.  Amer.  Acad.,  26,  268.     1891. 


SULPHUR.  83 


Na2CO3.  Na2SO±.  Ratio. 

1.29930  I.74H3  134.005 

3.18620  4.26790  133-950 

1.01750  1.36330  133.985 

2.07680  2.78260  I33-985 

1.22427  1.63994  I33-952 

1.77953  2.38465  134.005 

2.04412  2.73920  134.004 

3.06140  4.10220  I33.997 


Mean,  133.985,  ±  .0055 

The  available  ratios  for  sulphur  are  now  as  follows : 

(l.)  Ag2  :  Ag.2S  :  :  loo  :  114.8581,  ±  .0006 
(2.)   Per  cent.  Ag  in  Ag2SO4,  69.205,  dz  .oou 
(3.)   2  AgCl  :  Ag2S  :  :  100  :  86.4733,  ±  -O011 
(4.)  Na2C03  :  Na2SO4  :  :  100  :  133.985,  =fc  -OO55 

From  these  ratios,  four  values  for  the  atomic  weight  of  sulphur  are 
deducible.  Calculating  with — 

O  =  15.879,  rt  .0003 
Ag  =  107.108,  ±  .0031 

Cl     -==  35.179,  ±  .0048 

Na  =  22.88l,  ±  .0046 
C  =  II.92O,  rb  .0004 
AgCl  =  142.287,  ±  .0037, 

we  have : 

From  (i) S  =  31.828,  =b  .0016 

From  (2) "  =  31.806,  zb  .0048 

From  (3) "  =  31.864,  i  .0086 

From  (4) "  =  31.835,^1.0191 

General  mean S  =  31.828,  ±  .0015 

If  0  =  16,  S  =  32.070.  From  Stas'  ratios  alone,  Stas  found  32.074; 
Ostwald,  32.0626;  Van  der  Plaats,  (A)  32.0576,  (B)  32.0590,  and  Thorn- 
sen,  32.0606.  Here  again  Stas'  determinations  far  outweigh  all  others. 


84  THE    ATOMIC    WEIGHTS. 


LITHIUM. 

The  earlier  determinations  of  the  atomic  weight  of  lithium  by  Arfved- 
son,  Stromeyer,  C.  G.  Gmelin,  and  Kralovanzky  were  all  erroneous, 
because  of  the  presence  of  sodium  compounds  in  the  material  employed. 
The  results  of  Berzelius,  Hagen,  and  Hermann  were  also  incorrect,  and 
need  no  further  notice  here.  The  only  investigations  which  we  need  to 
consider  are  those  of  Mallet,  Diehl,  Troost,  Stas,  and  Dittmar. 

Mallet's  experiments*  were  conducted  upon  lithium  chloride,  which 
had  been  purified  as  completely  as  possible.  In  two  trials  the  chloride 
was  precipitated  by  nitrate  of  silver,  which  was  collected  upon  a  filter 
and  estimated  in  the  ordinary  way.  The  figures  in  the  third  column 
represent  the  LiCl  proportional  to  100  parts  of  AgCl : 

7.1885  grm.  LiCl  gave  24.3086  grm.  AgCl.  29.606 

8.5947  "  29.0621  29.574 

In  a  third  experiment  the  LiCl  was  titrated  with  a  standard  solution 
of  silver.  3.9942  grm.  LiCl  balanced  10.1702  grm.  Ag,  equivalent  to 
13.511  grm.  AgCl.  Hence  100  AgCl  =  29.563  LiCl.  Mean  of  all  three 
experiments,  29.581,  ±  .0087. 

Diehl.f  whose  paper  begins  with  a  good  resume  of  all  the  earlier 
determinations,  describes  experiments  made  with  lithium  carbonate. 
This  salt,  which  was  spectroscopically  pure,  was  dried  at  130°  before 
weighing.  It  was  then  placed  in  an  apparatus  from  which  the  carbon 
dioxide  generated  by  the  action  of  pure  sulphuric  acid  upon  it  could  be 
expelled,  and  the  loss  of  weight  determined.  From  this  loss  the  follow- 
ing percentages  of  C02  in  Li2C03  were  determined : 

59.422 
59.404 
59.440 
59.401 


Mean,  59.417,  ±  .006 

Diehl's  investigation  was  quickly  followed  by  a  confirmation  from 
Troost.J  This  chemist,  in  an  earlier  paper,§  had  sought  to  fix  the  atomic 
weight  of  lithium  by  an  analysis  of  the  sulphate,  and  had  found  a  value 
not  far  from  6.5,  thus  confirming  the  results  of  Berzelius  and  of  Hagen, 
who  had  employed  the  same  method.  But  Diehl  showed  that  the  BaS04 
precipitated  from  Li.2S04  always  retained  traces  of  Li,  which  were  recog- 

*  Silliman's  Amer.  Journal,  November,  1856.     Chem.  Gazette,  15,  7. 

f  Ann.  Chem.  Pharm.,  121,  93. 

JZeit.  Anal.  Chem.,  i,  402. 

I  Annales  d.  Chim.  et  d.  Phys.,  51,  108. 


LITHIUM.  85 

nizable  by  spectral  analysis,  and  which  accounted  for  the  error.  In  the 
later  paper  Troost  made  use  of  the  chloride  and  the  carbonate  of  lithium, 
both  spectroscopically  pure.  The  carbonate  was  strongly  ignited  with 
pure  quartz  powder,  thus  losing  carbon  dioxide,  which  loss  was  easily 
estimated.  The  subjoined  results  were  obtained  : 

.97ogrm.  Li2CO3  lost    .577  grm.  CO2.  59-485  per  cent. 

1.782  "  1.059         "  59.427       " 

Mean,  59.456,  ±  .020 

The  lithium  chloride  employed  by  Troost  was  heated  in  a  stream  of 
dry  hydrochloric  acid  gas,  of  which  the  excess,  after  cooling,  was  ex- 
pelled by  a  current  of  dry  air.  The  salt  was  weighed  in  the  same  tube 
in  which  the  foregoing  operations  had  been  performed,  and  the  chlorine 
was  then  estimated  as  silver  chloride.  The  usual  ratio  between  LiCl 
and  100  parts  of  AgCl  is  given  in  the  third  column  : 

1.309  grm.  LiCl  gave  4.420  grm.  AgCl.  29  615 

2.750  "  9.300         "  29.570 


Mean,  29.5925,  ±  .0145 

This,  combined  with  Mallet's  mean,  29.581,  ±  .0087,  gives  a  general 
mean  of  59.584,  ±  .0075. 

Next  in  order  is  the  work  of  Stas,*  which  was  executed  with  his  usual 
wonderful  accuracy.  In  three  titrations,  in  which  all  the  weights  were 
reduced  to  a  vacuum  standard,  the  following  quantities  of  LiCl  balanced 
100  parts  of  pure  silver  : 

39.356 

-39-357 

39-361 

Mean,  39.358,  ±  .001 

In  a  second  series  of  experiments,  intended  for  determining  the  atomic 
weight  of  nitrogen,  LiCl  was  converted  into  LiN03.  The  method  was 
that  employed  for  a  similar  purpose  with  the  chlorides  of  sodium  and 
of  potassium.  One  hundred  parts  of  LiCl  gave  of  LiN03: 

162.588 
162.600 
162.598 

Mean,  162.5953,  dr  .0025 

The  determinations  of  Dittmarf  resemble  those  of  Diehl;  but  the 
lithium  carbonate  used  was  dehydrated  by  fusion  in  an  atmosphere  of 
carbon  dioxide.  The  carbonate  was  treated  with  sulphuric  acid,  and 

*  Aroiistein's  translation,  279-302. 

t  Trans.  Roy.  Soc.  Edinburgh,  35,  II,  429.     1889. 


86  THE    ATOMIC    WEIGHTS. 

the  C02  was  collected  and  weighed  in  an  absorption  apparatus,  which 
was  tared  by  a  similar  apparatus  after  the  method  of  Regnault.  The 
following  percentages  of  CO2  in  Li2C03  were  found  : 

59.601 
59.645 

59.529— rejected. 

59.655 
59.683 
59.604 

59.517 

59.663 

60.143 — rejected. 

59-794 

59-584 


Mean  of  all,  59.674 

Rejecting  the  two  experiments  which  Dittmar  regards  as  untrust- 
worthy, the  mean  of  the  remaining  nine  becomes  59.638,  ±  .0173.  This 
combines  with  the  work  of  Diehl  and  Troost,  as  follows : 

Diehl 59.417,  =b  .0060 

Troost 59.456,  ±  .0200 

Dittmar 59.638,  db  .0173 


General  mean 59.442,  =b  .0054 

Dittmar's  determinations  give  a  much  lower  value  for  the  atomic 
weight  of  lithium  than  any  of  the  others,  and  therefore  seem  to  be  ques- 
tionable. As,  however,  they  carry  little  weight  in  the  general  combina- 
tion, it  is  not  necessary  to  speculate  upon  their  possible  sources  of  error. 

The  ratios  for  lithium  are  now  as  follows': 

(l.)  AgCl  :  LiCl  :  :  100  :  29.584,  ±  .0075 

(2.)  Ag  :  LiCl  :  :  100  :  39.358,  ±  .001. 

(3.)  LiCl  :  LiNO3  :  :  100  :  162.5953,  ±  .0025 

(4.)  Per  cent,  of  CO2  in  Li2CO3,  59.442,  ±  .0054 

And  the  data  to  use  in  their  reduction  are — 

O   --   15.879,  ±  .0003  N      —   13.935,  =t  .0015 

Ag— 107.108,  ±  .0031  C        =    11.920,  db  .0004 

Cl  ==    35-179,  ±.0048  AgCl=  142.287,  ±.0037 

These  factors  give  two  values  for  the  molecular  weight  of  lithium 
chloride,  thus  : 

From  (i) LiCl  =  42.0942,  ±  .01 10 

From  (2) «     =42.1556,  ±.0016 


General  mean LiCl  =  42. 1542,  ±  .0016 


RUBIDIUM.  87 

For  lithium  itself  there  are  three  values  : 

From  molecular  weight  LiCl Li  =  6.9752,  ±  .0051 

From  (3^ "  —  6.9855,  ±  .0129 

From  (4) "  —  6.9628,  d=  .0077 


General  mean Li  r=  6.9729,  ±  .0040 

If  0  —  16,  Li  =-  7.026.  From  Stas'  ratios,  Stas  found  Li  =  7.022  ;  Ost- 
wald,  7.0303;  Van  cler  Plaats  (A),  7.0273;  (B),  7.0235;  and  Thomsen, 
7.0307. 


RUBIDIUM. 

i 

The  atomic  weight  of  rubidium  has  been  determined  by  Bunsen,  Pic- 
card,  Godeffroy,  and  Hey  cock  from  analyses  of  the  chloride  and  bromide. 

Bunsen,*  employing  ordinary  gravimetric  methods,  estimated  the  ratio 
between  AgCl  and  RbCl.  His  rubidium  chloride  was  purified  by  frac- 
tional crystallization  of  the  chloroplatinate.  He  obtained  the  following 
results,  to  which,  in  a  third  column,  I  add  the  ratio  between  RbCl  and 
100  parts  of  AgCl : 

One  grm.  RbCl  gave  1.1873  grm.  AgCl.  84.225 

1.1873          "  84.225 

1.1850          "  84.388 

I. 1880          "  84.175 

Mean,  84.253,  db  .031 

The  work  of  Piccardf  was  similar  to  that  of  Bunsen.  In  weighing, 
the  crucible  containing  the  silver  chloride  was  balanced  by  a  precisely 
similar  crucible,  in  order  to  avoid  the  correction  for  displacement  of  air. 
The  filter  was  burned  separately  from  the  AgCl,  as  usual ;  but  the  small 
amount  of  material  adhering  to  the  ash  was  reckoned  as  metallic  silver. 
The  rubidium  chloride  was  purified  by  Bunsen's  method.  The  results, 
expressed  according  to  the  foregoing  standard,  are  as  follows : 

I-1S&7  Srm-  RbCl=  1.372  AgCl  -f-  .0019  Ag.  84.300 

1.4055         "  1.6632    "        .0030  "  84.303 

i. ooi  "  1.1850    "          .0024    "  84.245 

"  1-7934    "          .0018    "  84.313 


Mean,  84.290,  d=  .0105 
Godeffroy,  J   starting   with   material  containing  both  rubidium  and 

*Zeit.  Anal.  Chem.,  i,  136.     Poggend.  Annal.,  113,  339.     1861. 

f Journ.  fur  Prakt.  Chem.,  86,  454.     1862.     Zeit.  Anal.  Chem.,  i,  518. 

I  Ann.  Chem.  Pharm.,  181,  185.     1876. 


88  THE    ATOMIC    WEIGHTS. 

caesium,  separated  the  two  metals  by  fractional  crystallization  of  their 
alums,  and  obtained  salts  of  each  spectroscopicalty  pure.  The  nitric 
acid  employed  was  tested  for  chlorine  and  found  to  be  free  from  that 
impurity,  and  the  weights  used  were  especially  verified.  In  two  of  his 
analyses  of  RbCl  the  AgCl  was  handled  by  the  ordinary  process  of  nitra- 
tion. In  the  other  two  it  was  washed  by  decantation,  dried,  and  weighed 
in  a  glass  dish.  The  usual  ratio  is  appended  in  the  third  column  : 


1.4055  grm.  RbCl  gave  1.6665  grm-  AgCl.  84.338 

1.8096          "  2.1461  84320 

2.2473  "  2.665  "  84.326 

2.273  "  2.6946         "  84.354 

Mean,  84.3345,  ±  .0051 

Combining  the  three  series,  we  get  the  following  result  : 

Bunsen  .................  84.253,    ±.031         Rb  =  84.7O2 

Piccard  .................   84.290,    ±.0105         "   1=84.754 

Godeffroy  ...............   84.3345,  dz  .0051         "    =84.817 


General  mean 84.324,    =fc  .0045 

Heycock*  worked  by  two  methods,  but  unfortunately  his  results  are 
given  only  in  abstract,  without  details.  First,  silver  solution  was  added 
in  slight  deficiency  to  a  solution  of  rubidium  chloride,  and  the  excess 
of  the  latter  was  measured  by  titration.  The  mean  of  seven  experiments 
gave — 

Ag  :  RbCl  :  :  107.93  :  120.801 

Hence  Rb  =  84.702. 

Two  similar  experiments  with  the  bromide  gave — 

Ag  :  RbBr  :  :  107.93  :  165.437 
Ag  :  RbBr  :  :  107.93  :  1^>S'34-2 


Mean,  165.3895,  ±  .0320 

There  are  now  three  ratios  for  the  metal  rubidium,  as  follows : 

(i.)   AgCl  :  RbCl  :  :  loo  :  84.324,  ±  .0045 

(2.)  Ag  :  RbCl  :  :  107.93  :  120.801 

(3.)  Ag  :  RbBr  :  :  107.93  •'  l65-3895>  ±  -°32° 

To  reduce  these  ratios  we  have — 

Ag  =  107.108,  zb  .0031 
Br  =  79.344,  ±  .0062 
C1  =  35-T79,  ±  -0048 
AgCl  =  142.287,  zh  .0037 

*  British  Association  Report,  1882,  p.  499. 


CAESIUM.  89 

For  the  molecular  weight  of  RbCl,  two  values  are  calculable : 

From  (i) RbCl=  119.981,  +  .0109 

From  (2) "      —  119.881,  ±  .0218 

General  mean RbCl  =  119.961,  =b  .0097 

To  the  value  from  ratio  (2)  I  have  arbitrarily  assigned  a  weight  rep- 
resented by  the  probable  error  as  written  above.  The  data  for  system- 
atic weighting  are  deficient,  and  no  other  course  of  procedure  seemed 
advisable. 

From  RbCl Rb  =  84.782,  ±  .0109 

From  RbBr,  ratio  (3) "    —  84.786,  ±  .0329 


General  mean Rb  =r  84.783,  ±  .0103 

If  0  =  16  Rb  — 85.429. 


CESIUM. 

The  atomic  weight  of  caesium,  like  that  of  rubidium,  has  been  deter- 
mined from  the  analysis  of  the  chloride.  The  earliest  determination, 
by  Bunsen,*  was  incorrect,  because  of  impurity  in  the  material  employed. 

In  1863  Johnson  and  Allen  published  their  results.f  Their  material 
was  extracted  from  the  lepidolite  of  Hebron,  Maine,  and  the  caesium  was 
separated  from  the  rubidium  as  bitartrate.  From  the  pure  caesium 
bitartrate  caesium  chloride  was  prepared,  and  in  this  the  chlorine  was 
estimated  as  silver  chloride  by  the  usual  gravimetric  method.  Reducing 
their  results  to  the  convenient  standard  adopted  in  preceding  chapters, 
we  have,  in  a  third  column,  the  quantities  of  CsCl  equivalent  to  100 
parts  of  AgCl : 

I-8371  grm-  CsCl  gave  1.5634  grm.  AgCl.  '              117.507 

2.1295              "              i. Si  n           "  n7-58° 

2.7018              "              2.2992           "  117-511 

1.56165            "              1.3302           "(  "7-399 

Mean,  117.499,  ±  .025 

Shortly  after  the  results  of  Johnson  and  Allen  appeared  a  new  series 
of  estimations  was  published  by  Bunsen.  J  His  caesium  chloride  was 
purified  by  repeated  crystallizations  of  the  chloroplatinate,  and  the  ordi- 

*Zeit.  Anal.  Chem.,  i,  137. 

f  Atner.  Journ.  Sci.  and  Arts  (2),  35,  94. 

J  Poggend.  Annalen,  119,  i.     1863. 


90  THE    ATOMIC    WEIGHTS, 

nary  gravimetric  process  was  employed.     The  following  results  represent, 
respectively,  material  thrice,  four  times,  and  five  times  purified : 

1.3835  grm.  CsCl  gave  1.1781  grm.  AgCl.      Ratio,  117.435 
1.3682  "  1.1644  "  "       117.503 

1.2478  "  1.0623  <l  "       117.462 


Mean,  117.467,  ±  .013 

Godeffroy's  work*  was,  in  its  details  of  manipulation,  sufficiently 
described  under  rubidium.  In  three  of  the  experiments  upon  caesium 
the  silver  chloride  was  washed  by  decantation,  and  in  one  it  was  col- 
lected upon  a  filter.  The  results  are  subjoined  : 

1.5825  grm.  CsCl  gave  1.351     grm.  AgCl.  Ratio,  117.135 

1.3487               "               1.1501         "  "       117.265 

1.1880               "                1.0141         "  "       117.148 

1.2309               "               1.051           "  "       117.107 


Mean,  117.164,  =b  .023 

We  may  now  combine  the  three  series  to  form  a  general  mean  : 

Johnson  and  Allen 117.499,  ±  .025         Cs  =  132.007 

Bunsen 117.467,^.013          "  =131.961 

Godeffroy 117.164,1^.023          "=131.560 

General  mean..  .    117.413,  dz  .010 

Hence,  if  AgCl  =  142.287,  ±  .0037,  and  Cl  =  35.179,  ±  .00-48,  Cs  = 
131.885,  ±  .0142. 

If  0=16,  Cs  — 132.890. 

*  Ann.  Chem.  Pharm.,  181,  185.     1876. 


COPPER.  91 


COPPER. 

The  atomic  weight  of  copper  has  been  chiefly  determined  by  means  of 
{he  oxide,  the  sulphate,  and  the  bromide,  and  by  direct  comparison  of 
the  metal  with  silver. 

.In  dealing  with  the  first-named  compound  all  experimenters  have 
agreed  in  reducing  it  with  a  current  of  hydrogen,  and  weighing  the 
metal  thus  set  free. 

The  earliest  experiments  of  any  value  were  those  of  Berzelius,*  whose 
results  were  as  follows : 

7.68075  grm.  CuO  lost  1.55    grm.  O.          79.820  per  cent.  Cu  in  CuO. 
9.6115  "  1.939       "    .  79.826          "  " 

Mean,  79.823,  ±  .002 

Erdmann  and  Marchand,f  who  come  next  in  chronological  order, 
corrected  their  results  for  weighing  in  air.  Their  weighings,  thus  cor- 
rected, give  us  the  subjoined  percentages  of  metal  in  CuO  : 

63.8962  grm.  CuO  gave  51.0391  grm.  Cu.  79.878  per  cent. 

65.1590  "  52-0363         "  79-860       " 

60.2878  48.1540         "  79.874       " 

46.2700  36.9449         "  79.846       " 

Mean,  79.8645,  =fc  .0038 

Still  later  we  find  a  few  analyses  by  Millon  and  Commaille.  J  These 
chemists  not  only  reduced  the  oxide  by  hydrogen,  but  they  also  weighed, 
in  addition  to  the  metallic  copper,  the  water  formed  in  the  experiments. 
In  three  determinations  the  results  were  as  follows  : 

6.7145  grm.  CuO  gave  5.3565  grm.  Cu  and  1.5325  grm.  H2O.       79-775  per  cent. 
3-39*5  "  2.7085  "  .7680         "  79.791       " 

2.7880  "  2.2240  "  79.770       " 


Mean,  79.7787,  rb  .0043 

For  the  third  of  these  analyses  the  water  estimation  was  not  made, 
but  for  the  other  two  it  yielded  results  which,  in  the  mean,  would  make 
the  atomic  weight  of  copper  62.680.  This  figure  has  so  high  a  probable 
error  that  we  need  not  consider  it  further. 

The  results  obtained  by  Dumas  §  are  wholly  unavailable.  Indeed,  he 
does  not  even  publish  them  in  detail.  He  merely  says  that  he  reduced 
copper  oxide,  and  also  effected  the  synthesis  of  the  subsulphide,  but  with- 
out getting  figures  which  were  wholly  concordant.  He  puts  Cu  =  63.5. 

*Poggend.  Annal.,  8,  177.     1826. 
t  Journ.  fur  Prakt.  Chem.,  31,  380.     1844. 
|  Fresenius'  Zeitschrift,  2,  475.     1863. 
I  Ann.  Chim.  et  Phys.  (3),  55,  129.     1859. 


92  THE    ATOMIC    WEIGHTS. 

In  1873  Hampe*  published  his  careful  determinations,  which  were 
for  many  years  almost  unqualifiedly  accepted.  First,  he  attempted  to 
estimate  the  atomic  weight  of  copper  by  the  quantity  of  silver  which 
the  pure  metal  could  precipitate  from  its  solutions.  This  attempt  failed 
to  give  satisfactory  results,  and  he  fell  back  upon  the  old  method  of 
reducing  the  oxide.  From  ten  to  twenty  grammes  of  material  were 
taken  in  each  experiment,  and  the  weights  were  reduced  to  a  vacuum 
standard : 

20.3260  grm.  CuO  gave  16.2279  grm.  Cu.  79.838  Per  cent. 

20.68851  "  16.51669       "  79.835        " 

10.10793  "  8.06926       "  79-831        " 

Mean,  79.8347,  rfc  .0013 

Hampe  also  determined  the  quantity  of  copper  in  the  anhydrous  sul- 
phate, CuS04.  From  40  to  45  grammes  of  the  salt  were  taken  at  a  time, 
the  metal  was  thrown  down  by  electrolysis,  and  the  weights  were  all 
corrected.  I  subjoin  the  results  : 

40.40300  grm.  CuSO4  gave  16.04958  grm.  Cu.       39.724  per  cent. 
44.64280  "  17.73466        "  39-726 

Mean,  39.725,  ±  .0007 

The  last  series  of  data  gives  Cu  =62.839,  ±  .0035,  and  is  interesting 
for  comparison  with  results  obtained  by  Richards  later. 

In  all  of  the  foregoing  experiments  with  copper  oxide,  that  compound 
was  obtained  by  ignition  of  the  basic  nitrate.  But,  as  was  shown  in  the 
chapter  upon  oxygen,  copper  oxide  so  prepared  always  carries  occluded 
gases,  which  are  not  wholly  expelled  by  heat.  This  point  was  thoroughly 
worked  up  by  Richards  f  in  his  fourth  memoir  upon  the  atomic  weight 
of  copper,  and  it  vitiates  all  the  determinations  previously  made  by  this 
method. 

By  a  series  of  experiments  with  copper  oxide  ignited  at  varying  tem- 
peratures, and  with  different  degrees  of  heat  during  the  process  of  reduc- 
tion, Richards  obtained  values  for  Cu  ranging  from  63.20  to  63.62,  when 
,  O  =  16.  In  two  cases  selected  from  this  series  he  measured  the  amount 
of  gaseous  impurity,  and  corrected  the  results  previously  obtained.  The 
results  were  as  follows,  with  vacuum  standards : 

1.06253  grm«  CuO  gave.     .84831  grm.  Cu.  79.802  per  cent. 

1.91656  "  1.5298  "  79.820       " 

Mean,  79.811,  ±  .0061 

Correcting  for  the  occluded  gases  in  the  oxide,  the  sum  of  the  two 
experiments  gives  79.901  per  cent,  of  copper,  whence  Cu  =  63.605.  Three 

*  Fresenius'  Zeitschrift,  13,  352. 
fProc.  Amer.  Acad.,  26,  276.     1891. 


COPPER.  93 

other  indirect  results,  similarly  corrected,  gave  79.900  per  cent.  Cu  in 
CuO,  or  Cu  =  63.603.  If  we  assign  all  five  experiments  equal  weight, 
and  judge  their  value  by  the  two  detailed  above,  the  mean  percentage 
becomes  79.900,  dt  .0038.  This  figure  need  not  be  combined  with  the 
data  given  by  previous  observers,  so  far  as  practical  purposes  are  con- 
cerned ;  but  as  this  work  is,  in  part  at  least,  a  study  of  the  compensation 
of  errors,  it  may  not  be  wasted  time  to  effect  the  combination,  as  follows : 

Berzelius 79.823,     ±  .0020 

Erdmann  and  Marchand 79.8645,  ±  .0038 

Millon  and  Commaille 79-7787,  ±  .0043 

Hampe 79-8347,  db  .0013 

Richards 79-9°°,    ±  .0038 


General  mean 79-8355,  ±  .0010 

This  result  is  practically  identical  with  that  of  Hampe,  whose  work 
receives  excessive  weight,  as  does  also  that  of  Berzelius.  The  oxide  of 
copper  is  evidently  of  doubtful  value  in  the  measurement  of  this  atomic 
weight. 

The  composition  of  the  sulphate  has  been  studied,  not  only  by  Hampe, 
but  also  by  Baubigny*  and  by  Richards.f  Baubigny  merely  ignited 
the  anhydrous  salt,  weighing  both  it  and  the  residual  oxide,  as  follows  : 

4.022  grm.  CuSO4  gave  2.0035  CuO.  49.813  per  cent. 

2.596  «  1.293       "  49.807        " 

Mean,  49.810,  ±  .002 

The  same  ratio,  in  reverse — that  is,  the  synthesis  of  the  sulphate  from 
the  oxide — was  investigated  by  Richards  (p.  275),  who  shows  that  the 
results  obtained  are  vitiated  by  the  same  errors  which  affect  the  copper 
oxide  experiments  previously  cited.  The  weights  given  are  reduced  to 
vacuum  standards.  The  percentage  of  oxide  in  the  sulphate  is  stated  in 
the  third  column  of  figures. 

1.0084  grm.  CuO  gave  2.0235  Srm-  CuSO4.  49-835  Per  cent. 

2.7292  5-4770  "  49.830       " 

1.0144  2.°35°  49.848       " 

Mean,  49.838,  ±  .0036 

The  two  series  combine  thus : 

Baubigny 49.810,  ±  .0020 

Richards.. , 49.838,  ±  .0036 


General  mean 49.816,  dr  .0017 

Here,  plainly,  the  rigorous  discussion  gives  Baubigny 's  work  weight 
in  excess  of  its  merits. 

*  Compt.  Rend.,  97,  906.     1883. 
fProc.  Amer.  Acad.,  26,  240.     1891. 


94  THE    ATOMIC    WEIGHTS. 

In  the  memoir  by  Richards  now  under  consideration,  his  fourth  upon 
copper,  the  greater  part  of  his  attention  is  devoted  to  the  sulphate, 
Hampe  being  followed  closely  in  order  to  ascertain  what  sources  of 
error  affected  the  work  of  the  latter.  Crystallized  sulphate,  CuS04.5H2O 
was  purified  with  every  precaution  and  made  the  basis  of  operations. 
Three  series  of  experiments  were  carried  out,  the  water  being  determined 
by  loss  of  weight  upon  heating,  and  the  copper  being  estimated  electro- 
lytically.  In  the  first  series  the  following  data  were  found,  the  weights 
being  reduced  to  a  vacuum,  as  in  all  of  Richards'  determinations : 

CuSO±.  5  aq.        CuSO±  at  250°.  Cu. 

i 2.8815  .7337 

2 2.7152  .6911 

3 3-4639  2.2184  .8817 

Hence  the  subjoined  percentages. 

Water  at  250°.  Cu  in  Ciyst.  Salt.  Cu  in  CuSOr 

i 25.462  

2 25.452  

3 35-95*  25.454  39.745 


Mean,  25.456 

In  the  second  series  of  analyses,  which  are  stated  with  much  detail, 
several  Tefinements  were  introduced,  in  order  to  estimate  also  the  sul- 
phuric acid.  These  will  be  considered  later.  The  results,  given  below, 
are  numbered  consecutively  with  the  former  series. 


aq.  CuSO^at  260°.  CuSO^atjdo0.  Cu. 

4  ......  .  ...............       3.06006                 1-9597                     1.95637  .77886 

5  ........................      2.81840                1.8048                   .  ......  .71740 

6  ........................      7-5°490                4-8064                    4.79826  1-90973 

Hence  percentages  as  follows  : 

Water,  260°.    Water,  360°.    Cu  in  Ciyst.  Salt.  Cu  in  CuSO±,  260°.  Ditto,  360.° 

4  ......      35-959               36.068                25.452                       39-744  39.8n 

5  ......      35.964                                          25.454                       39-750  ...... 

6  ......      35-957               36-065                25.446     f                  39-733  39-799 

Mean,  35.960  '  36.067  25.450  39-742  39.805 

Hampe  worked  with  a  sulphate  dried  at  250°,  but  these  data  show  that 
a  little  water  is  retained  at  that  temperature,  and  consequently  that  his 
results  must  have  been  too  low.  The  third  of  Richards'  series  resembles 
the  second,  but  extra  precautions  were  taken  to  avoid  conceivable  errors. 

CuSO±.  5  aq.  CitSO±  at  260°.  CuSO4  at  370°.  Cu. 

7  ....................  •      -      2.88307                .......                  .......  .73380 

8  ........................      3.62913               2.32373                  .......  .92344 

9  ........................      5.8I352                .......                  3.71^80  1.47926 


COPPER.  95 

And  the  percentages  are : 

Water  at  260°.     At  j/o0.     Cu  in  Cryst.  Salt.     Cu  in  CuSOt. 

7 25.452  

8 35-970  25.446  39.740(260°) 

9 36.067  25.445  39-799(370°) 

25.448 

In  this  series  the  determinations  of  sulphuric  acid  gave  essentially  the 
same  results  for  all  three  samples  of  sulphate,  although  one  was  not 
dehydrated,  and  the  others  were  heated  to  260°  and  370°  respectively. 
Hence  the  loss  of  weight  in  dehydration  at  either  temperature  represents 
water  only,  and  does  not  involve  partial  decomposition  of  the  sulphate. 
Between  360°  and  400°  copper  sulphate  is  at  essentially  constant  weight, 
but  further  experiments  indicated  that  even  at  400°  it  retained  traces  of 
water,  and  possibly  as  much  as  .042  per  cent.  The  last  trace  is  not  ex- 
pelled until  the  salt  itself  begins  to  decompose. 

Richards  also  effected  two  syntheses  of  the  sulphate  directly  from  the 
metal  by  dissolving  the  latter  in  nitric  acid,  then  evaporating  to  dryness 
with  sulphuric  acid,  and  heating  to  constant  weight  at  400°. 

.67720  grm.  Cu  gave  1.7021  grm.  CuSO4.  39-786  per  cent.  Cu. 

1.00613  "  2.5292  "  39.78i  " 

If  we  include  these  percentages  in  a  series  with  the  data  from  analyses 
4,  6,  and  9,  which  gave  percentages  of  39.811,  39.799,  and  39.799  respect- 
ively of  copper  in  sulphate  dried  at  360°  and  upwards,  the  mean  becomes 

CuSO4  :  Cu  :  :  100  :  39.795,  ±  .0036 

Since  even  this  result  is  presumably  too  low,  the  other  figures  from 
sulphate  dried  at  250°  must  be  rejected.  Since  Hampe's  work  on  the 
sulphate  is  affected  by  the  same  sources  of  error,  and  apparently  to  a 
still  greater  extent,  it  need  not  be  considered  farther.  As  for  Richards' 
nine  determinations  of  Cu  in  CuS04.5H20,  we  may  take  them  as  one 
series  giving  a  mean  percentage  of  25.451,  ±  .0011.  This  salt  seems  to 
retain  occluded  water,  for  the  percentage  of  copper  in  it  leads  to  a  value 
for  the  atomic  weight  which  is  inconsistent  with  the  best  evidence,  as 
will  be  seen  later. 

In  the  second  and  third  series  of  Richards'  experiments  upon  copper 
sulphate,  the  sulphuric  acid  was  estimated  by  a  method,  which  gave 
valuable  results.  After  the  copper  had  been  electrolytically  precipitated, 
the  acid  which  was  set  free  was  nearly  neutralized  by  a  weighed  amount 
of  pure  sodium  carbonate,  and  the  slight  excess  remaining  was  deter- 
mined by  titration.  Thus  the  weight  of  sodium  carbonate  equivalent  to 
the  copper  was  ascertained.  The  resulting  solution  of  sodium  sulphate 
was  then  evaporated  to  dryness,  and  a  new  ratio,  connecting  that  salt 
with  copper,  was  also  determined.  The  cross  ratio  Na2C03 :  Na2S04  has 


96  THE   ATOMIC   WEIGHTS. 

already  been  utilized  in  a  previous  chapter.  The  results,  ignoring  the 
weights  of  h  yd  rated  copper  sulphate,  are  as  follows,  with  the  experiments 
numbered  as  before  : 

Cu.  Na2COs.  JVa2SOi 

4 • 77886  1.2993  1.7411 

6 1.90973  3.1862  4.2679 

7 7338o  1.22427  1.63994 

8 92344  L54075 

9 1.47926  3.30658 

Hence, 

Cu  :  Na.yCO^  '•  :  IOO  :  x.  Cu  :  Na.1SO^  :  :  IOO  :  x. 
166.824  223.549 

166.840  223.482 

166.840  223.538 

166.849  223.529 

Mean,  166.838,  ±  .0035  Mean,  223.525,  ±  .0098 

In  one  more  experiment  the  sulphuric  acid  was  weighed  as  barium 
sulphate,  the  latter  being  corrected  for  occluded  salts.  3.1902'  grin. 
CuSO,.5H20  gave  2.9761  BaSO, ;  hence  CuS04.5H20  :  BaS04  :  :  100 : 
93.289.  The  sulphate  contained  25.448  per  cent,  of  Cu  ;  hence  BaS04 : 
Cu  : :  93.289:  25.448.  Still  other  ratios  can  be  deduced  from  Richards1 
work  on  the  sulphate,  but  in  view  of  the  uncertainties  relative  to  the 
water  in  the  salt  they  are  hardly  worth  computing. 

In  his  third  paper  upon  the  atomic  weight  of  copper,*  Richards  studied 
the  dibromide,  CuBr.2.  In  preparing  this -salt  he  used  hydrobromic 
acid  made  from  pure  materials,  and  further  purified  by  ten  distillations. 
This  was  saturated  with  copper  oxide  prepared  from  pure  electrolytic 
copper,  and  the  solution  obtained  was  proved  to  be  free  from  basic  salts. 
As  the  crystallized  compound  was  not  easily  obtained  in  a  satisfactory 
condition,  weighed  quantities  of  the  solution  were  taken  for  analysis,  in 
which,  after  expulsion  of  bromine  by  nitric  and  sulphuric  acids,  the 
copper  was  determined  by  electrolysis.  In  other  portions  of  solution 
the  bromine  was  precipitated  by  silver  nitrate,  and  weighed  as  silver 
bromide.  The  first  preliminary  series  of  experiments  gave  the  subjoined 
results,  with  vacuum  weights  as  usual : 

In  3d  Grammes  of  Solution. 

Cu.  AgBr. 

.4164  2.4599 

.4.164  2.4605 

.4164  2.4605 

.4165  2.4599 

Hence  2  AgBr  :  Cu  :  :  100  : 16.927,  ±  .0013. 

*  Proc.  Amer.  Acad.,  25,  195.     1890. 


COPPER.  97 

The  second,  also  preliminary  series,  was  made  with  more  dilute  solu- 
tions, and  came  out  as  follows: 

In  25  Grammes  of  Solution. 

Cu.  AgBr. 

.26190  1.5478 

.26185  1-5477 

1-5479 

Hence  2  AgBr :  Cu  :  :  100 :  16.919,  ±  .0012. 

In  the  third  series,  two  distinct  lots  of  crystallized  bromide  were  dis- 
solved, and  the  solutions  examined  in  the  same  way. 

Cu.  AgBr.  Ratio. 

.2500  i.477i  16.925 

•  5473  3.2348  16.919 


Mean,  16.922,  =b  .0020 

In  the  final  set  of  analyses,  the  materials  used  were  purified  even  more 
scrupulously  than  before,  and  the  process  was  distinctly  modified,  as 
regards  the  determination  of  the  bromine.  The  solution  of  the  bromide 
was  added  to  a  solution  of  pure  silver  in  nitric,  acid,  not  quite  sufficient 
for  complete  precipitation.  The  slight  excess  of  bromine  was  then 
determined  by  titration  with  a  solution  containing  one  gramme  of  silver 
to  the  litre.  Thus  silver  proportional  to  the  copper  in  the  bromide  was 
determined,  and  the  silver  bromide  was  weighed  in  a  Gooch  crucible  as 
before.  The  results  are  subjoined : 

In  50  Grammes  of  Solution. 

Cu.                                Ag.  AgBr. 

.54755                               I-8586  3.235o 

.54750                               !-8579  3-2340 

1.8583  3-2348 

Hence  Cu :  Ag, :  -100  :  339.392,  ±  .0108,  and  2  AgBr  :  Cu  : :  100 :  16.927, 
±  .0012. 

The  latter  ratio,  combined  with  the  results  of  the  three  preceding  series, 
gives  a  general  mean  of : 

2  AgBr  :  Cu  :  :  100  :  16.924,  ±  .0007 

In  his  two  earlier  papers  *  Richards  determined  the  Qopper-silver  ratio 
directly — that  is.  without  the  weighing  of  any  comp^u^iq;G?f»ej,ther  metal. 
By  placing  pure  copper  in  an  ice-cold  solution .o^-sijyer  *£Srq,te*  metallic 
silver  is  thrown  down,  and  the  weights  of  the  tw.D/fnetals-  were 

*Proc.  Atner.  Acad.,  22,  346,  and  23,  177.     1886  and  1887".  *,»,""  > 


98  THE    ATOMIC   WEIGHTS. 

alent  proportions.     In  the  first  paper  the  following  results  were  obtained. 
The  third  column  gives  the  value  of  x  in  the  ratio  Cu  :  Ag.2 :  :  100  :  x. 

Cu  Taken.  Ag  Found.  Ratio. 

.53875  I-8292  339.527 

.56190  1.9076  339-491 

1.00220  3.4016  339.414 

1.30135  4.4173  339.440 

•99s7o  3.39035  339-477 

1.02050  3.4646  '  339.500 

Mean,  339.475,  =h  .0114 

In  the  second  paper  Richards  states  that  the  silver  of  the  fifth  experi- 
ment, which  had  been  dried  at  150°,  as  were  also  the  others,  still  retained 
water,  to  the  extent  of  four-tenths  milligramme  in  two  grammes.  If  we 
assume  this  correction  to  be  fairly  uniform,  as  the  concordance  of  the 
series  indicates,  and  apply  it  throughout,  the  mean  value  for  the  ratio 
then  becomes  339.408,  ±  .0114.  This  procedure,  however,  leaves  the 
ratio  in  some  uncertainty,  and  accordingly  some  new  determinations 
were  made,  in  which  the  silver,  collected  in  a  Gooch  crucible,  was  heated 
to  incipient  redness  before  final  weighing.  Copper  from  two  distinct 
sources  was  taken,  and  three  experiments  were  carried  out  upon  one 
sample  to  two  with  the  other.  Treating  both  sets  as  one  series,  the 
results  were  as  follows  : 

Cu  Taken.  Ag  found.  Ratio. 

.7576o  2.5713  339.40 

.95040  3-2256  339-39 

•  75993  2.5794  339-42 

1.02060  3-4640  339-42 

.90460  3.0701  339-39 


Mean,  339.404,  d=  .0046 

a  value  practically  identical  with  the  corrected  mean  of  the  previous 
determinations,  and  w7ith  that  found  in  the  later  experiments  upon 
copper  bromide. 

In  various  electrical  investigations  the  same  ratio,  the  electrochemical 
equivalent  of  copper,  has  been  repeatedly  measured,  and  the  later  results 
of  Lord  Rayleigh  and  Mrs.  Sidgewick,*  Gray,f  Shaw,  %  and  Vanni  §  may 
properly  be  included  in  this  discussion.  As  the  data  are  somewhat  dif- 
ferently stated,  I  have  reduced  them  all  to  the  common  standard  adopted 
above.  Gray  gives  'two  sets  of  measurements,  one  made  with  large  and 
the  other  w.ith^syiigill;  metallic  plates  : 

»  '     '  T'r      ''',*  Phil.  7>an 


•  r    %  British  A3soc.  Report,  1886.    Abstract  in  Phil.  Mag.  (5),  23,  138. 
T'r   '  rr^A?fn'  der  Phys.  (Wiedemanu's)  (2),  44,  214. 


COPPER. 


99 


Rayleigh  and  S. 
340.483 
340.832 

340.367 

Gray  i. 
341.297 

34L4I3 
340.815 
340.252 

339-905 
341.064 
340.832 
341.297 
341.064 
34L4I3 

Gray  2. 
340.252 

339.674 
340.020 

339.905 
339-674 
339-328 
340.136 
340.136 
340.136 
340.020 
340.020 
340.136  ' 

Shaiu. 
339-68 
340.05 
339.84 
339-71 
340.04 

339-94 
340.35 
339.82 
340.09 
339.84 
339.90 
339.98 
340.H 
340.56 
339-82 

340.56r, 
±  .0935 

340.935, 
±  .  1072 

339-953, 
±  .0521 

Vanni. 
340.483 
340.600 

340.367 
340.252 
340.600 
340.136 

340.406, 
±  .0520 


The  lack  of  sharp  concordance  in  these  data  and  the  consequently 
high  probable  errors  seem  to  indicate  a  distinct  superiority  of  the  purely 
chemical  method  of  determination  over  that  adopted  by  the  physicist. 
The  eight  distinct  series  now  combine  as  follows : 

Richards,  first  series  corrected 339-4°8,  ±  .0114 

Richards,  second  series ...  339.404,  ±  .0046 

Richards,  CuBr2  series .  339.392,  =b  .0108 

Rayleigh  and  Sidgewick 340.561,  d=  .0935 

Gray,  with  large  plates 34°-935,  ^  .  1072 

Gray,  with  small  plates 339-953,  ±  .0521 

Shaw . ..  339.983,  =b  .0411 

Vanni 340.406,  ±  .0520 

General  mean 339-41 1,  ±  .0039 

If  we  combine  Richards'  three  series  into  a  general  mean  separately, 
we  get  339.402,  ±  .0040.  Hence  the  other  determinations,  having  high 
>robable  errors,  practically  vanish  from  the  result,  and  it  is  a  matter  of 
idifference  whether  they  are  retained  or  rejected. 

We  now  have  the  following  ratios  from  which  to  compute  the  atomic 
.'eight  of  copper : 

(i.)  Percentage  of  Cu  in  CuO 79-8355,  ±  .0010 


(2.) 

(3-) 
(4.) 

(5.)  Cu 
(6.)  Cu 


of  Cu  in  CuSO4 39-795,    =fc  -0036 

of  Cu  in  CuSO4,  5H2O. .   25.451,    ±  .0011 
of  CuO  in  CuSO4 49-8i6,  ^±-.0017 


Na,CO, 


Na2SO4  : 


100 

IOO 


166.838,  ±  .0035 

223.525,  =fc  .0098  • 
(7.)   BaSO4  :  Cu  :  :  93-289  :  25-448- 
(8.)   2AgBr  :  Cu  :  :  IOO  :  16.924,  ±  .0007 


(9- 


:  Ag2 


.0039 


100  THE    ATOMIC    WEIGHTS. 

Reducing  these  ratios  with  the  subjoined  data  : 

O  -  =   15.879,  ±  .0003  Na       _   22.881,  ±  .0046 

Ag—  107.108,  ±  .0031  Ha  =  136.392,  =h  .0086 
S  =  31.828,  ±  .0015  AgBr  =  186.452,  =b  .0054 
C  =  11.920,  d-  .0004 

We  have  nine  values  for  the  atomic  weight  of  .copper.  Since  ratio  (7) 
depends  upon  one  experiment  only,  it  is  necessary  to  assign  the  value 
derived  from  it  arbitrary  weight.  This  will  be  taken  as  indicated  by  a 
probable  error  double  that  of  the  next  highest,  obtained  from  ratio  (.2). 
The  values  then  are  as  follows  : 

From  (i)  .........................  Cu  =  62.869,  d=  .0034 

From  (2)  ..........................  "    =  63.022,  db  .0070 

From  (3)  ..........................  <(  =  63.070,  ±  .0030 

From  (4)  .........................  "  =63.003,  ±  .0042 

From  (5)  ..........................  "  =63.127,  d=  .0051 

From  (6)..  ,  .......................  "  =  63.128,  ±  .0050 

From  (7)  ................  ..........  "   —  63.215,  ±  .0140 

From  (8)  ..............    ...........  "  =  63.  1  10,  ±  .0032 

From  (9)  ..........................  "  =63.  114,  ±  .0020 

General  mean  ................   Cu  —  63.070,  d=  .0012 

If  O  =  16,  Cu  =  63.550.  If  we  include  Hampe's  analyses  of  copper 
sulphate,  which  gave  Cu  =  62.839,  ±  .0035,  the  general  mean  becomes 
Cu  —  63.046,  ±.0011. 

The  foregoing  means,  however,  are  significant  only  as  showing  the 
effect  and  weight  of  the  older  data  upon  the  newer  determinations  of 
Richards.  The  seventh  of  the  individual  values  is  also  interesting,  for 
the  reason  that  the  experiment  upon  which  it  depends  was  published  by 
Richards  previous  to  his  investigation  of  the  atomic  weight  of  barium. 
With  the  old  value  for  Ba,  137,  it  gives  a  value  for  copper  in  close  agree- 
ment with  Richards'  other  determinations.  With  the  new  value  for 
barium  it  becomes  discordant,  although  its  weight  is  so  low  that  it  pro- 
duces no  appreciable  effect  upon  the  final  mean. 

Rejecting  values  1  to  4,  inclusive,  the  remaining  five  values  give  a  gen- 
eral mean  of 

Cu  ==63.119,  rfc  .0015. 

If  0  =  16,  this  becomes  63600,  and  in  the  light  of  all  the  evidence 
these  figures  are  to  be  preferred.  If,  again,  we  combine  with  this  mean 
the  results  of  Richards'  work  on  the  oxide  and  sulphate  of  copper,  the 
final  value  becomes 

,  \\  \\  '',  ;  Cu  =  63.108,  ±  .0013, 


with  0  =  16f  $8$$$.'%  This  departs  but  little  from  the  previous  mean 
'.value',  'bu^it'i'H'el'uclee'  'data  which  render  it,  in  all  probability,  a  trifle  too 
low,  l^h'p/v^Hie  Cu  =  63.119  will  be  regarded  as  the  best. 


GOLD.  101 


GOLD. 

Among  the  early  estimates  of  the  atomic  weight  of  gold  the  only  ones 
worthy  of  consideration  are  those  of  Berzelius  and  Levol. 

The  earliest  method  adopted  by  Berzelius*  was  that  of  precipitating 
a  solution  of  gold  chloride  by  means  of  a  weighed  quantity  of  metallic 
mercury.  The  weight  of  gold  thus  thrown  down  gave  the  ratio  between 
the  atomic  weights  of  the  two  metals.  In  the  single  experiment  which 
Berzelius  publishes,  142.9  parts  of  Hg  precipitated  93.55  of  Au.  Hence 
if  Hg  =  200,  Au  =  196.397. 

In  a  later  investigation  f  Berzelius  resorted  to  the  analysis  of  potassio- 
auric  chloride,  2KC1.  A  uCl3.«  Weighed  quantities  of  this  salt  were  ignited 
in  hydrogen  ;  the  resulting  gold  and  potassium  chloride  were  separated 
by  means  of  water,  and  both  were  collected  and  estimated.  The  loss  of 
weight  upon  ignition  was,  of  course,  chlorine.  As  the  salt  could  not  be 
perfectly  dried  without  loss  of  chlorine,  the  atomic  weight  under  inves- 
tigation must  be  determined  by  the  ratio  between  the  KC1  and  the  Au. 
If  we  reduce  to  a  common  standard,  and  compare  with  100  parts  of  KC1, 
the  equivalent  amounts  of  gold  will  be  those  which  I  give  in  the  last  of 
the  subjoined  columns : 

4.1445  grm.  K2AuCl5  gave  .8185  grm.  KC1  and  2.159  grm-  Au.  263.775 

2.2495  .44425  "  i.»72  "  263-8l5 

5  1300  "  1.01375  "  2.67225      "  263.600 

3.4130  "  .674  "  1.77725       "  263.687 

4.19975  .8295  "  2.188  263.773 

Mean,  263.730,  ±  .026 

Still  a  third  series  of  experiments  by  Berzelius  $  may  be  included 
here.  In  order  to  establish  the  atomic  weight  of  phosphorus  he  em- 
ployed that  substance  to  precipitate  gold  from  a  solution  of  gold  chloride 
in  excess.  Between  the  weight  of  phosphorus  taken  and  the  weight  of 
gold  obtained  it  was  easy  to  fix  a  ratio.  Since  the  atomic  weight  of 
phosphorus  has  been  better  established  by  other  methods,  we  may 
properly  reverse  this  ratio  and  apply  it  to  our  discussion  of  gold.  100 
parts  of  P  precipitate  the  quantities  of  Au  given  in  the  third  column : 

.829  grm.  P  precipitated  8.714  grm.  Au.  1051.15 

.754  "  7-93°         "  1051.73 


Mean,  1051.44,  d=  .196 

Hence  if  P  =  31,  Au  =  195.568. 

*  Poggend.  Annalen,  8,  177. 
f  Lehrbuch,  5  Aufl.,  3,  1212. 
J  Lehrbuch,  5  Aufl.,  3,  1188. 


102  THE    ATOMIC    WEIGHTS. 

Level's  *  estimation  of  the  atomic  weight  under  consideration  can 
hardly  have  much  value.  A  weighed  quantity  of  gold  was  converted 
in  a  flask  into  AuCl3.  This  was  reduced  by  a  stream  of  sulphur  dioxide,. 
and  the  resulting  sulphuric  acid  was  determined  as  BaS04.  One  gramme 
of  gold  gave  1,782  grin.  BaS04.  Hence  Au  =  195.06. 

All  these  values  may  be  neglected  as  worthless,  except  that  derived 
from  Berzelius'  K2AuCl5  series. 

In  1886  Kriissf  published  the  first  of  the  recent  determinations  of  the 
atomic  wreight  under  consideration,  several  distinct  methods  being  re- 
corded. First,  in  a  solution  of  pure  auric  chloride  the  gold  was  pre- 
cipitated by  means  of  aqueous  sulphurous  acid.  In  the  filtrate  from  the 
gold  the  chlorine  was  thrown  down  as  silver  chloride,  and  thus  the  ratio 
Au :  3  AgCl  was  measured.  I  subjoin  Kriiss'  weights,  together  with  a 
third  column  giving  the  gold  equivalent  to  1QO  parts  of  silver  chloride: 

Au.  AgCl.  Ratio. 

7.72076  16.84737  45-828 

5.68290  12.40425  45.814 

3.24773  7.08667  45-828 

4.49167  980475  45-8ii 

3-47949  7-59300  45-825 

3.26836  7  13132  45-832 

5.16181  11.26524  45.821 

4.86044  10.60431  45.834 

Mean,  45.824,  ±  .0020 

The  remainder  of  Kruss'  determinations  were  made  with  potassium 
auribromide,  KAuBr4,  and  with  this  salt  several  ratios  were  measured. 
The  salt  was  prepared  from  pure  materials,  repeatedly  recrystallized 
under  precautions  to  exclude  access  of  atmospheric  dust,  and  dried  over 
phosphorus  pentoxide.  First,  its  percentage  of  gold  was  determined, 
sometimes  by  reduction  with  sulphurous  acid,  sometimes  by  heating  in 
a  stream  of  hydrogen.  For  this  ratio,  the  weights  and  percentages  are 
as  follows,  the  experiments  being  numbered  for  further  reference,  and  the 
reducing  agent  being  indicated. 

KAuBr±.  Au.  Per  cent. 

i.  SO, 10.64821  3-77753  35476 

2-  S02 4.71974  1.67330  35-453 

3-  H 7-05762  2.50122  35-440 

4.   H 4-49558  1-59434  35-465 

5-  SO, 8.72302  3-09448  35-475 

6.  SO2 7.66932  2.71860  35-448 

7-  SO, 7.15498  2.53695  35.457 

8-  H 12.26334  4-34997  35-471 

9-  II 7-10342  2.51919  35-465 

Mean,  35.461,  ±  .0028 

- — —  — , , 

*  Ann.  Chim.  Phys.  (3),  30,  355.     1850. 
"t  Untersuchungen  uber  das  Atomgewicht  des  Goldes.     Mi'mchen,  1886.     112  pp.,  Svo. 


GOLD.  103 

In  five  of  the  foregoing  experiments  the  reductions  were  effected  with 
sulphurous  acid ;  and  in  these,  after  filtering  off  the  gold,  the  bromine 
was  thrown  down  and  weighed  as  silver  bromide.  This,  in  comparison 
with  the  gold,  gives  the  ratio  Au  :  4AgBr  :  :  100  :  x. 

Au.  <j.AgBr>  Ratio. 

i 3-77753  H.39542  381.080 

2 1.67330  6.37952  381.254 

5 3-09448  ".78993  380.999 

6   2.71860  10.35902  381.042 

7 2.53695  9.66117  380.731 

Mean,  381.021,  ±.  .057 

Hence  Au  :  AgBr  :  :  100  :  95.255,  ±  .0142. 

In  the  remaining  experiments,  Nos.  3,  4,  8,  and  9,  the  KAuBr4  was 
reduced  in  a  stream  of  hydrogen,  the  loss  of  weight,  Br3,  being  noted. 
In  the  residue  the  gold  was  determined,  as  noted  above,  and  the  KBr 
was  also  collected  and  weighed.  The  weights  were  as  follows  : 

Au.  Loss,  Brz.  KBr. 

3 2.50122  3-04422  1.51090 

4 1-59434  1-93937  -96243 

8   4-34997  5-293l6  2.62700 

9 2.51919  3-06534  L52I53 

From  these  data  we  obtain  two  more  ratios,  viz.,  Au  :  Br3  :  :  100  :  SB, 
and  Au  :  KBr  :  :  100  :  x,  thus : 

Au  :  Brz.  Au  :  KBr. 

3   121.710  60.405 

4 121.641  60.365 

8 121.683  60.391 

9 121.680  60.398 


Mean,  121.678,  ±  .0100         Mean,  60.390,  ±  .0059 

From  all  the  ratios,  taken  together,  Krtiss  deduces  a  final  value  of 
Au  =  197.13,  if  0  =  16.  It  is  obviously  possible  to  derive  still  other 
ratios  from  the  results  given,  but  to  do  so  would  be  to  depart  unneces- 
sarily from  the  author's  methods  as  stated  by  himself. 

Thorpe  and  Laurie,  *  whose  work  appeared  shortly  after  that  of  Kruss, 
also  made  use  of  the  salt  KAuBr4,  but,  on  account  of  difficulty  in  drying 
it  without  change,  they  did  not  weigh  it  directly.  After  proving  the  con- 
stancy in  it  of  the  ratio  Au  :  KBr,  even  after  repeated  crystallizations, 
they  adopted  the  following  method  :  The  unweighed  salt  was  heated 
with  gradual  increase  of  temperature,  up  to  about  160°,  for  several  hours, 
and  afterwards  more  strongly  over  a  small  Bunsen  flame.  This  was  done 
in  a  porcelain  crucible,  tared  by  another  in  weighing,  which  latter  was 
treated  in  precisely  the  same  way.  The  residue,  KBr  -f  Au,  was  weighed, 
the  KBr  dissolved  out,  and  the  gold  then  weighed  separately.  The 

*  Journ.  Chein.  Soc.,  51,  565.     1887. 


104 


THE   ATOMIC    WEIGHTS. 


weightjof  KBr  was  taken  by  difference.     The  ratio  Au:KBr:  :  100 :  x 

appears  in  a  third  column. 

An.                                   KBr.  Ratio. 

6.19001                             3-73440  60.329 

4.76957                             2.87715  60.32? 

4.14050                             2.49822  60.336 

3.60344                             2.17440  60.342 

3.67963                             2.21978  60.326 

4-57757                              2.76195  60.337 

5-36659                              3-23821  60.326 

5.16406                              3. 11533  60.327 

Mean,  60.331,  ±  .0016 

This  mean  combines  with  Krtiss'  thus: 

Kriiss 60.390,  ±  .0059 

Thorpe  and  Laurie 60.331,  d=  .0016 


General  mean 60.338,  d=  .0015 

The  potassium  bromide  of  the  previous  experiments  was  next  titrated 
with  a  solution  of  pure  silver  by  Stas'  method,  the  operation  being 
performed  in  red  light.  Thus  we  get  the  following  data  for  the  ratio 
Ag  :  Au  :  :  100  :  :c,  using  the  weights  of  gold  already  obtained  : 

Ag.  Au.  Ratio. 

3.38451  6.19001  182.893 

2.60896  4.76957  182.813 

2.28830  4.18266  182.786 

2.26415  4.14050  182.868 

1.97147  3-60344  182.775 

2.01292  3-67963  182.801 

2.50334  4-57757  182.863 

2.93608  5.36659  182.780 

2.82401  5.16406  182.865 


Mean,  182.827,  ±  .0101 

Finally,  in  eight  of  these  experiments,  the  silver  bromide  formed 
during  titration  was  collected  and  weighed,  giving  values  for  the  ratio 
Au:  AgBr: 


100  :  x,  as  follows : 

An.  AgBr. 

6.19001  5.89199 

4.76957  4-54261 

4.18266  3.98288 

4.14050  3-94309 

3-60344  3-430i5 

3.67963  3-50207 

4.57757  4.35736 

5.36659  5-11045 


Ratio. 

95.186 
95.242 

95-224 
95.232  , 

95.i9i 
95-175 
95-189 
95.227 

Mean,  95.208,  ±  .0061 
Kriiss  found,  95.255,  dr  .0142 


General  mean,  95.222,  ±  .0056 


GOLD.  105 

From  the  second  and  third  of  the  ratios  measured  by  Thorpe  and 
Laurie  an  independent  value  for  the  ratio  Ag  :  Br  may  be  computed.  It 
becomes  100  :  74.072,  which  agrees  closely  with  the  determinations  made 
by  Stas  and  Marignac.  Similarly,  the  ratios  Ag  :  KBr  and  AgBr  :  KBr 
may  be  calculated,  giving  additional  checks  upon  the  accuracy  of  the 
manipulation,  though  not  upon  the  purity  of  the  original  material 
studied. 

Thorpe  and  Laurie  suggest  objections  to  the  work  done  by  Kriiss,  on 
the  ground  that  the  salt  KAuBr4  cannot  be  completely  dried  without 
loss  of  bromine.  This  suggestion  led  to  a  controversy  between  them  and 
Kriiss,  which  in  effect  was  briefly  as  follows : 

First,  Kriiss*  urges  that  the  potassium  auribromide  ordinarily  contains 
traces  of  free  gold,  not  belonging  to  the  salt,  produced  by  the  reducing 
action  of  dust  particles  taken  up  from  the  air.  He  applies  a  correction 
for  this  supposed  free  gold  to  the  determinations  made  by  Thorpe  and 
Laurie,  and  thus  brings  their  results  into  harmony  with  his  own.  To 
this  argument  Thorpe  and  Laurie  f  reply,  somewhat  in  detail,  stating 
that  the  error  indicated  was  guarded  against  by  them,  and  that  they 
had  dissolved  quantities  of  from  eight  to  nineteen  grammes  of  the  auri- 
bromide without  a  trace  of  free  gold  becoming  visible.  A  final  note  in 
defense  of  his  own  work  was  published  by  Kriiss  a  little  later.  J 

In  1889  an  elaborate  set  of  determinations  of  this  constant  was  pub- 
lished by  Mallet,  §  whose  experiments  are  classified  into  seven  distinct 
series.  First,  a  neutral  solution  of  auric  chloride  was  prepared,  which 
was  weighed  off  in  two  approximately  equal  portions.  In  one  of  these 
the  gold  was  precipitated  by  pure  sulphurous  acid,  collected,  washed, 
dried,  ignited  in  a  Sprengel  vacuum,  and  weighed.  To  the  second  por- 
tion a  solution  containing  a  known  weight  of  pure  silver  was  added. 
After  filtering,  with  all  due  precautions,  the  silver  remaining  in  the  fil- 
trate was  determined  by  titration  with  a  weighed  solution  of  pure  hydro- 
bromic  acid.  We  have  thus  a  weight  of  gold,  and  the  weight  of  silver 
needed  to  precipitate  the  three  atoms  of  chlorine  combined  with  it;  in 
other  words,  the  ratio  Ag3  :  Au  :  :  100  :  x.  All  weights  in  this  and  the 
subsequent  series  are  reduced  to  vacuum  standards,  and  all  weighings 
were  made  against  corresponding  tares. 

Au.  Agy  Ratio. 

7.6075  12.4875  60.921 

8.4212  13.8280  60.900 

6.9407  ir-3973  60.898 

3.3682  5.5286  60.923 

2.8244  4.6371  60.909 

Mean,  60.910,  ±  .0034 

Hence  Ag  :  Au  :  :  100  :  182.730,  ±  .0102. 

*Ber.  Deutsch.  Chem.  Gesell.,  20,  2365.     1887. 
fBerichte,  20,  3036,  and  Journ.  Chem.  Soc.,  51,  866.     1887. 
t  Berichte,  21,  126.     1888. 
%  Philosophical  Transactions,  180,  395.     1889. 


106  THE    ATOMIC    WEIGHTS. 

The  second  series  of  determina.tions  was  essentially  like  the  first,  ex- 
cept that  auric  bromide  was  taken  instead  of  the  chloride.  The  ratio 
measured,  Ag3 :  Au,  is  precisely  the  same  as  before.  Results  as  follows  : 

Au.  Agy  Ratio. 

8.2345  13-5149  60.929 

7.6901  12.6251  60.911 

105233  17.2666  60.945 

2.7498  4.5141  60.916 

3.5620  5-8471  60.919 

3.9081  6.4129  60.941 


Mean,  60.927,  ±  .0038 

Hence  Ag  :  Au : :  100 : 182.781,  ±  .0114. 

In  the  third  series  of  experiments  the  salt  KAuBr4was  taken,  purified 

by  five  recrystallizations.     The  solution  of  this  was  weighed  out  into 

nearly  equal  parts,  the  gold  being  measured  as  in  the  two  preceding 

series  in  one  portion,  and  the  bromine  thrown  down  by  a  standard  silver 

solution  as  before.     This  gives  the  ratio  Ag4 :  Au  : :  100  :  x. 

Au.  Ag.  Ratio. 

5.7048  12.4851  45.693 

7.9612  I7.4I93  45-693 

2-4455  5.35!3  45-699 

4.1632  9-"53  45-673 

Mean,  45.689,  ±  .0040  . 

Hence  Ag :  Au  : :  100 : 182.756,  ±  .0160. 

The  fifth  series  of  determinations,  which  for  present  purposes  naturally 
precedes  the  fourth,  was  electrolytic  in  character,  gold  and  silver  being 
simultaneously  precipitated  by  the  same  current.  The  gold  was  in  solu- 
tion as  potassium  auro-cyanide,  and  the  silver  in  the  form  of  potassium 
silver  cyanide.  The  equivalent  weights  of  the  two  metals,  thrown  down 
in  the  same  time,  were  as  follows,  giving  directly  the  ratio  Ag :  Au : :  100 :  x. 
Au.  Ag.  Ratio. 

5.2721  2.8849  182.748 

6.3088  3.4487  182.933 

4.2770  2.3393  182.832 

3-5I23  1.9223  182.713 

3.6804  2.0132  182.814 

Mean,  182.808,  ±  .0256 

This  mean  may  be  combined  with  the  preceding  means,  and  also  with 
the  determination  of  the  same  ratio  by  Thorpe  and  Laurie,  thus  : 

Thorpe  and  Laurie 182.827,  ±  .0.101 

Mallet,  chloride  series 182.730,  ±  .0102 

Mallet,  bromide  series 182.781,  ±  .01 14 

Mallet,  KAuBr4  series 182  756,  ±  .0160 

Mallet,  electrolytic 182.808,  ±  .0256 

General  mean 182.778,  =h  .0055 


GOLD.  107 

Iii  Mallet's  fourth  series  a  radically  new  method  was  employed.  Tri- 
m ethyl-ammonium  aurichloride,  N(CH3)3HAuCl4,  was  decomposed  l»y 
heat,  and  the  residual  gold  was  determined.  In  order  to  avoid  loss  by 
spattering,  the  salt  was  heated  in  a  crucible  under  a  layer  of  fine  siliceous 
sand  of  known  weight.  Several  crops  of  crystals  of  the  salt  were  studied, 
as  a  check  against  impurities,  but  all  gave  concordant  values. 

Salt.  Residual  Au.  Percent.  A u. 

14-9072  7-3754  49-475 

15.5263  7.6831  49-484 

10.4523  5-1712  49-474 

6.5912  3.2603  49.464 

5-5744  2.7579  49-474 


Mean,  49.474,  ±  .0021 

In  his  sixth  and  seventh  series  Mallet  seeks  to  establish,  by  direct 
measurement,  the  ratio  between  hydrogen  and  gold.  In  their  experi- 
mental details  his  methods  are  somewhat  elaborate,  and  only  the  pro- 
cesses, in  the  most  general  way,  can  be  indicated  here.  First,  gold  was 
precipitated  electrolytically  from  a  solution  of  potassium  aurocyanide, 
and  its  weight  was  compared  with  that  of  the  amount  of  hydrogen  simul- 
taneously liberated  in  a  voltameter  by  the  same  current  in  the  same 
time.  The  hydrogen  was  measured,  and  its  weight  was  then  computed 
from  its  density.  The  volumes  are  given,  of  course,  at  0°  and  760  mm. 

Wt.  Au.  Vol.  H,  cc.  Wt.  H. 

4.0472                              228.64  .°2°5483 

4.0226                              227.03  .0204046 

4.0955                              231.55  ,      .0208103 

These  data,  with  the  weight  of  one  litre  of  hydrogen  taken  as  0.89872 
gramme,  give  the  subjoined  values  in  the  ratio  H  :  Au  :  :  1  :  x. 

196.960 

197-151 
196.805 


Mean,  196.972,  =b  .0675 

In  the-last  series  of  experiments  a  known  quantity  of  metallic  zinc  was 
dissolved  in  dilute  sulphuric  acid,  and  the  amount  of  hydrogen  evolved 
was  measured.  Then  a  solution  of  pure  auric  chloride  or'bromide  was 
treated  with  a  definite  weight  of  the  same  zinc,  and  the  quantity  of  gold 
thrown  down  was  determined.  The  zinc  itself  was  purified  by  practical 
distillation  in  a  Sprengel  vacuum.  From  these  data  the  ratio  H3 :  Au 
was  computed  by  direct  comparison  of  the  weight  of  gold  and  that  of  the 
liberated  hydrogen.  The  results  were  as  follows  : 


108 


THE    ATOMIC    WEIGHTS. 


Wt.  Au. 

10.3512 
8.2525 
8.1004 

3-2913 

3.4835 
3.6421 


Vol.  H,  cc. 

1756.10 

1400.38 

1374.87 

558.64 

590-93 


Wt.  H. 

.157824 
•125857 

.123565 
.050206 
.053109 
•055551 


Hence  for  the  ratio  H3 :  Au  :  :  1 :  x  we  have  : 

65-587 
65-571 
65.557 
65.556 
65o93 
65.563 


Mean,  65.571,  ±.00436 

And  H  :  Au  :  :  1  : 196.713,  ±  .0131.     This,  combined  with  the  value 
found  in  the  preceding  series,  gives  a  general  mean  of  196.722,  ±  .0129. 
The  ratios  available  for  gold  are  now  as  follows : 

(l.)  2KC1  :  Au  :  :  100  :  263.730,  ±  .026 

(2-)  3^gCl  :  Au  :  :  100  :  45.824,  ±;  .0020 

(3.)  KAuBr4  :  Au  :  :  100  :  35.461,  db  .0028 

(4.)  Au  :  AgBr  :  :  100  :  95.222,  ±  .0056 


(5.)  Au  :  Br3  : 

(6.)  Au  :  KBr 

(7.)  Ag  :  Au  : 

(8. 

(9.)  H  :  Au 


:  IOO  :  121.678,  db  .OIOO 
:  :  TOO  :  60.338,  d=  0015 


100  :  182.778,  d=  -0055 

loo  :  49.474,  ±  .0021 
196.722,  dr  .0129 


For  the  reduction  of  these  ratios  the  antecedent  data  are : 


Ag=  107.108,  zb  .0031 
Cl  ==  35.179,  d=  .0048 
Br  =  79-344,  ±  .0062 
K  =  38.817,  d=  .0051 
N  =  J3.935,  ±  .0021 


C  =  11.920,  dr  .0004 
AgCl  —  142.287,  ±  .0037 
AgBr  =  186.452,  d=  .0054 
KC1  =  74.025,  ±  .0019 
KBr  =  118.200,  ±  .0073 


Hence  for  the  atomic  weight  of  gold  we  have  nine  values  : 

From  (i) Au  =  195.226,  ±  .0193 


From  (2) 
From  (3) 
From  (4) 
From  (5) 
From  (6) 
From  (7) 
From  (8) 
From  (9) 


—  195.605,  d=  .0099 
=  I95-711,  ±  .0224 
=  195.808,  d=  .0126 

=  195.624,  ±  .0222 

=  T95-896,  db  .0131 
=  195.770,  db  .0082 
=  196.238,  =h  .0224 

=  196.722,  ±  .0129 


General  mean Au  =  195.850,  dz  .0044 

If  0  =  16,  this  becomes  Au  =  197.342. 


GOLD.  109 

Of  the  foregoing  values  the  first  one,  which  is  derived  from  Berzelius' 
work,  should  certainly  be  rejected.  So  also,  apparently,  should  the  eighth 
and  ninth  values.  Excluding  these,  values  2  to  7,  inclusive,  give  a  gen- 
eral mean  of  Au  =  195.743,  ±  .0049.  With  0  =  16,  this  becomes  Au  = 
197.235.  Probably  these  values  are  more  nearly  correct  than  those  which 
include  all  the  determinations. 

The  ninth  value  in  the  list  given  above  represents  Mallet's  comparisons 
of  gold  directly  with  hydrogen,  and  is  peculiarly  instructive.  In  Mal- 
let's paper  the  other  determinations  are  discussed  upon  the  basis  of 
O  =  15.96,  which  brings  them  more  nearly  into  harmony  with  the  hydro- 
gen series.  The  great  divergence  shown  in  this  recalculation  is  due  to 
the  new  value  for  oxygen,  15.879,  and  its  effect  upon  the  atomic  weights 
of  silver,  bromine,  etc.  The  former  agreement  between  the  several  series 
of  gold  values  was  therefore  only  apparent,  and  we  are  now  able  to  see 
that  concordance  among  determinations  maybe  only  coincidence,  and 
no  proof  of  accuracy.  It  is  probable,  furthermore,  that  direct  compari- 
sons of  metals  with  hydrogen  cannot  give  good  measurements  of  atomic 
weights,  for  several  reasons.  First,  it  is  not  possible  to  be  certain  that 
every  trace  of  hydrogen  has  been  collected  and  measured,  and  any  loss 
tends  to  raise  the  apparent  atomic  weight  of  the  metal  studied ;  secondly, 
the  weight  of  the  hydrogen  is  computed  from  its  volume,  and  a  slight 
change  in  the  factors  used  in  reduction  of  the  observations  may  make  a 
considerable  difference  in  the  final  result.  These  uncertainties  exist  in 
all  determinations  of  atomic  weights  hitherto  made  by  the  hydrogen 
method. 


110  THE    ATOMIC    WEIGHTS. 


CALCIUM. 

For  determining  the  atomic  weight  of  calcium  we  have  sets  of  experi- 
ments by  Berzelius,  Erdmann  and  Marchand,  and  Dumas.  Salvetat  * 
also  has  published  an  estimation,  but  without  the  details  necessary  to 
enable  us  to  make  use  of  his  results.  I  also  find  a  reference  f  to  some 
work  of  Marignac,  which,  however,  seems  to  have  been  of  but  little  im- 
portance. The  earlier  work  of  Berzelius  was  very  inexact  as  regards 
calcium,  and  it  is  not  until  we  come  down  to  the  year  1824  that  we  find 
any  material  of  decided  value. 

The  most  important  factor  in  our  present  discussion  is  the  composi- 
tion of  calcium  carbonate,  as  worked  out  by  Dumas  and  by  Erdmann 
and  Marchand. 

In  1842  Dumas  J  made  three  ignitions  of  Iceland  spar,  and  determined 
the  percentages  of  carbon  dioxide  driven  off  and  of  lime  remaining.  The 
impurities  of  the  material  were  also  determined,  the  correction  for  them 
applied,  and  the  weighings  reduced  to  a  vacuum  standard.  The  per- 
centage of  lime  came  out  as  follows  : 

56.12 
56.04 
56.06 


Mean,  56.073,  ±  .016 

About  this  same  time  Erdmann  and  Marchand  §  began  their  researches 
upon  the  same  subject.  Two  ignitions  of  spar,  containing  .04  per  cent, 
of  impurity,  gave  respectively  56.09  and  56.18  per  cent,  of  residue ;  but 
these  results  are  not  exact  enough  for  us  to  consider  further.  Four  other 
results  obtained  with  artificial  calcium  carbonate  are  more  noteworthy. 
The  carbonate  was  precipitated  from  a  solution  of  pure  calcium  chloride 
by  ammonium  carbonate,  was  washed  thoroughly  with  hot  water,  and 
dried  at  a  temperature  of  180°.  With  this  preparation  the  following 
residues  of  lime  were  obtained  : 

56.03 

55.98 

56.00 

55-99 
Mean,  56.00,  ±  .007 

It  was  subsequently  shown  by  Berzelius  that  calcium  carbonate  pre- 
pared by  this  method  retains  traces  of  water  even  at  200°,  and  that 


*Compt.  Rend.,  17,  318.     1843. 

fSee  Oudeman's  monograph,  p.  51. 

JCompt.  Rend.,  14,  537.     1842. 

g  Journ.  fur  Prakt.  Chem.,  26,  472.     1842. 


CALCIUM.  Ill 

minute  quantities  of  chloride  are  also  held  by  it.  These  sources  of  error 
are,  however,  in  opposite  directions,  since  one  would  tend  to  diminish 
and  the  other  to  increase  the  weight  of  residue. 

In  the  same  paper  there  are  also  two  direct  estimations  of  carbonic 
acid  in  pure  Iceland  spar,  which  correspond  to  the  following  percentages 
of  lime  : 

56.00 

56.02 

Mean,  56.01,  ±  .007 

In  a  still  later  paper*  the  same  investigators  give  another  series  of 
results  based  upon  the  ignition  of  Iceland  spar.  The  impurities  were 
carefully  estimated,  and  the  percentages  of  lime  are  suitably  corrected  : 

4.2134  grm.  CaCO3  gave  2.3594  grm.  CaO.  55-997  per  cent. 

15.1385  "  8.4810         "  56.022        " 

23.5503  "  13.1958          "  56-031        " 

23.6390.  I3-2456         "  56-°32 

42.0295  23.5533         "  56.044       " 

49.7007  "  27.8536         "  56.042       " 


Mean,  56.028,  ±  .0047 

Six  years  later  Erdmann  and  March  and  f  published  one  more  result 
upon  the  ignition  of  calcium  carbonate.  They  found  that  the  compound 
began  giving  off  carbon  dioxide  below  the  temperature  at  which  their 
previous  samples  had  been  dried,  or  about  200°,  and  that,  on  the  other 
hand,  traces  of  the  dioxide  were  retained  by  the  lime  after  ignition. 
These  two  errors  do  not  compensate  each  other,  since  both  tend  to  raise 
the  percentage  of  lime.  In  the  one  experiment  now  under  consideration 
these  errors  were  accurately  estimated,  and  the  needful  corrections  were 
applied  to  the  final  result.  The  percentage  of  residual  lime  in  this  case 
came  out  55.998.  This  agrees  tolerably  well  with  the  figures  found  in  the 
direct  estimation  of  carbonic  acid,  and,  if  combined  with  those  two.  gives 
a  mean  for  all  three  of  56.006,  ±  .0043. 

Combining  all  these  series,  we  get  the  following  result : 

Dumas 56.073,  ±  .016 

Erdmann  and  Marchand .  .    56.006,  rb  .007 

Erdmann  and  Marchand 56.028,  dr  .0047 

Erdmann  and  Marchand 56.006,  ±  .0043 


General  mean 56.0198,  ±  .0029 

For  reasons  given  above,  this  mean  is  probably  vitiated  by  a  slight 
instant  error,  which  makes  the  figure  a  trifle  too  high. 

*  Journ.  fur  Prakt.  Cheni.,  31,  269.     1844. 
•f  Journ.  fi'ir  Prakt.  Chem.,  50,  237.     1850. 


112  THE    ATOMIC    WEIGHTS. 

In  the  earliest  of  the  three  papers  by  Erdmann  and  Marchand  there  is 
also  given  a  series  of  determinations  of  the  ratio  between  calcium  car- 
bonate and  sulphate.  Pure  Iceland  spar  was  carefully  converted  into 
calcium  sulphate,  and  the  gain  in  weight  noted.  One  hundred  parts  of 

spar  gave  of  sulphate  : 

136.07 
136.06 
136.02 
136.06 

Mean,  136.0525,  ±  .0071 

In  1843  the  atomic  weight  of  calcium  was  redetermined  by  Berzelius,  * 
who  investigated  the  ratio  between  lime  and  calcium  sulphate.  The 
calcium. was  first  precipitated  from  a  pure  solution  of  nitrate  by  means 
of  ammonium  carbonate,  and  the  thoroughly  washed  precipitate  was 
dried  and  strongly  ignited  in  order  to  obtain  lime  wholly  free  from  ex- 
traneous matter.  This  lime  was  then,  with  suitable  precautions,  treated 
with  sulphuric  acid,  and  the  resulting  sulphate  was  weighed.  Correction 
was  applied  for  the  trace  of  solid  impurity  contained  in  the  acid,  but  not 
for  the  weighing  in  air.  The  figures  in  the  last  column  represent  the 
percentage  of  weight  gained  by  the  lime  upon  conversion  into  sulphate  : 

1.80425  grm.  CaO  gained  2.56735  grm.  142.295 

2.50400  "  3.57050     "  142.592 

3.90000  S-SSHO    "  142.343 

3.04250  "  4.32650     "  142.202 

3.45900  "  4- 93 HO    "  142.567 


Mean,  142.3998,  ±  .0518 

Last  of  all  we  have  the  ratio  between  calcium  chloride  and  silver,  as 
determined  by  Dumas,  t  Pure  calcium  chloride  was  first  ignited  in  a 
stream  of  dry  hydrochloric  acid,  and  the  solution  of  this  salt  was  after- 
wards titrated  with  a  silver  solution  in  the  usual  way.  The  CaCl2  pro- 
portional to  100  parts  of  Ag  is  given  in  a  third  column : 

2.738  grm.  CaCl2  =  5.309  grm.  Ag.  51-573 

2.436             "             4.731         "  5 '.490 

1.859                            3-6i7         "  5^396 

2.771                            5.38*5       "  5L424 

2.240             «            4.3585       "  5I-394 


Mean,  51.4554,  ±  .0230 

We  have  now  four  ratios  to  compute  from,  as  follows : 

(i.)  Percentage  CaO  in  CaCO3,  56.0198,  ±  .0029 

(2.)  CaO  :  SO3  :  :  100  :  142.3998,  ±  .0518 

(3.)  CaCO3  :  CaSO4  :  :  100  :  136.0525,  ±  .0071 

(4-)  Ag2  :  CaC]2  :  :  100  :  51.4554,  ±  .0230 

*  Journ.  fur  Prakt.  Chem.,  31,  263.     Ann.  Chem.  Pharm.,  46,  241. 
t  Ann.  Chim.  Phys.  (3),  55,  129.     1859.     Ann.  Chem.  Pharm.,  113,  34. 


STRONTIUM.  113 

The  antecedent  values  are  — 

O   =   15.879,  ±  .0003  c=  11.920,  ±  .0004 

Ag  =  107.108,  ±  .0031  S  =31.828,  ±  -0015 


Hence  the  subjoined  values  for  the  atomic  weight  of  calcium  : 

From  (i)  ..........................  Ca  =  39.757,  dz  .0048 

From  (2)  ...    ......................    "   =  39.925,  ±  .0203 

From  (3)  .................    ........    "   ==  39-706,  ±  .0204 

From  (4)  .........................    "    =  39.868,  HE  .0503 


Mean Ca  =  39.764,  ±  .0045 

If  0  =  16,  Ca  =  40.067. 


STRONTIUM. 

The  ratios  which  fix  the  atomic  weight  of  strontium  resemble  in  gen- 
eral terms  those  relating  to  barium,  only  they  are  fewer  in  number  and 
represent  a  smaller  amount  of  work.  The  early  experiments  of  Stro- 
meyer,*  who  measured  the  volume  of  CO2  evolved  from  a  known  weight 
of  strontium  carbonate,  are  hardly  available  for  the  present  discussion. 
So  also  we  may  exclude  the  determination  by  Salvetat,f  who  neglected 
to  publish  sufficient  details. 

Taking  the  ratio  between  strontium  chloride  and  silver  first  in  order, 
we  have  series  of  figures  by  Pelouze  and  by  Dumas.  Pelouze  J  employed 
the  volumetric  method  to  be  described  under  barium,  and  in  two  ex- 
periments obtained  the  subjoined  results.  In  another  column  I  append 
the  ratio  between  SrCl2  and  100  parts  of  silver  : 

1.480  grm.  SrCl2  =  2.014  grm.  Ag.  73-486 

2.210  "  3.008       "  73-471 


Mean,  73.4781,  db  .0050 

Dumas,  §  by  the  same  general  method,  made  sets  of  experiments  with 
three  samples  of  chloride  which  had  previously  been  fused  in  a  current 
of  dry  hydrochloric  acid.  His  results,  expressed  in  the  usual  way,  are 
as  follows : 

*  Schweigg.  Journ.,  19,  228.     1816. 

f  Compt.  Rend.,  17,  318      1843. 

I  Compt.  Rend.,  20,  1047.     1845. 

I  Ann.  Chim.  Phys.  (3),  55,  29.     1859.     Ann  Cheat.  Pharm.,  113,  34. 


114  THE   ATOMIC    WEIGHTS. 

Series  A. 

3.137  grm.  SrCl2  =  4.280  grm.  Ag.  Ratio,  73.2944 

1.982             "            2.705       "  "      73-27I7 

3.041                           4.142       "  «      73.4186 

3.099            "           4.219       «  "      73-4534 


Mean,  73-3595 
Series  B. 

3.356  grm.  SrCl2  =  4-574  grm.  Ag.           Ratio,  73-3713 

6.3645                        8.667       "                       «  73.4327 

7.131                          9.712       "                      »  73.4246 

Mean,  73.4095 
Series  C. 


7.213  grm.  SrC 

I2  —  9.811  grm.  Ag. 

Ratio,  73-5J95 

2.206             " 

3.006       " 

"      73.3866 

4.268 

5.816       " 

"      73.5529 

4.018             " 

5-477        " 

"      73.3613 

Mean,  73.455 1 
Mean  of  all  as  one  series,  73.4079,  ±  .0170 

Combining  these  data  we  have : 

Pelouze 73.478i,  rb  .0050 

Marignac 73.4079,  ±  .0170 


General  mean 73.4725,  zb  .0048 

The  foregoing  figures  apply  to  anhydrous  strontium  chloride.  The 
ratio  between  silver  and  the  crystallized  salt,  SrCl,.6H,O,  has  also  been 
determined  in  two  series  of  experiments  by  Marignac.*  Five  grammes 
of  salt  were  used  in  each  estimation,  and,  in  the  second  series,  the  per- 
centage of  water  was  first  determined.  The  quantities  of  the  salt  corre- 
sponding to  100  parts  of  silver  are  given  in  the  last  column  : 

Series  A. 

5  grm.  SrCl2.6H2O  =4.0515  grm.  Ag.  123.411 

4.0495       "  123.472 

4.0505        "  123.442 


Mean,  123.442 
Series  B. 

5  grm.  SrCl.2. 6 H2O  —  4.0490  grm.  Ag.  123.487 

4.0500        "  123.457 

4.049°       "  123.487 


Mean,  123.477 
Mean  of  all  as  one  series,  123.460,  ±  .0082 


*  Journ.  fur  Prakt.  Chem.,  74,  216.     1858. 


STRONTIUM. 


115 


In  the  same  paper  Marignac  gives  two  sets  of  determinations  of  the 
percentage  of  water  in  crystallized  strontium  chloride.  The  first  set,  cor- 
responding to  u  B  "  above,  is  as  follows : 

40.556 
40.568 
40.566 

Mean,  40.563 

In  the  second  set  ten  grammes  of  salt  w.ere  taken  at  a  time,  and  the 
following  percentages  were  found : 

40.58 

40.59 
40.58 


Mean,  40.583 
Mean  of  all  as  one  series,  40.573,  ±  .0033 

The  chloride  used  in  the  series  of  estimations  last  given  was  subse- 
quently employed  for  ascertaining  the  ratio  between  it  and  the  sulphate. 
Converted  directly  into  sulphate,  100  parts  of  chloride  yield  the  quanti- 
ties given  in  the  third  column  : 


5.942  grm.  SrCl2  gave  6.887  grm.  SrSO4. 
5-941  "  6.8855        " 

5.942  "  6.884 


II5-932 
i '5-949 
H5.927 

Mean,  115.936,  ±  .004 


Richards.*  in  his  study  of  strontium  bromide,  followed  pretty  much 
the  lines  laid  down  in  his  work  on  barium.  The  properties  of  the 
bromide  itself  were  carefully  investigated,  and  its  purity  established 
beyond  reasonable  doubt,  and  then  the  two  usual  ratios  were  deter- 
mined. First,  the  ratio  Ag2  :  SrBr2  :  :  100  :  x,  by  titration  with  standard 
solutions  of  silver.  For  this  ratio  there  are  three  series  of  measurements, 
by  varied  processes,  concerning  which  full  details  are  given.  The  data 
obtained,  with  weights  reduced  to  a  vacuum,  are  as  follows : 


First  Series. 


Wt.  Ag. 

1.30755 
2.10351 

2.23357 
5-3684 


Wt. 

1.49962 
2.41225 

2.56153 
6.15663 


Ratio. 
114.689 
114.677 
114.683 
114.683 


Mean,  114.683 
*  Proc.  Amer.  Acad.  of  Sciences,  1894,  p.  369. 


116 


THE    ATOMIC    WEIGHTS. 


Second  Series. 


Wt.  Ag. 
1.30762 
2.10322 
4-57502 
5.3680 


«.S434 
3-3957 
3.9607 

4.5750 


Wt. 
i.  49962 
2.41225 
5.24727 
6.15663 


Third  Series. 

2.9172 
3.8946 
4.5426 
5-2473 


Ratio. 

114.683 

114.693 

114.694 

114.691 

Mean,  114.690 


114.697 
1 14.692 
114.692 
114.695 


Mean,  114.694 
Mean  of  all  as  one  series,  114.689,  db  .0012 


For  the  ratio,  measured  gravimetrically,  2AgBr  :  SrBr2  :  :  100  :  x,  two 


series  of  determinations  are  given  : 

First  Series. 


Wt.  AgBr. 

2.4415 
2.8561 

6.9337 


2.27625 
3.66140 
3-88776 
9.34497 


Wt.  SrBr., 
i. 6086 
1.8817 
4.5681 


Second  Series. 

1.49962 
2.41225 

2.56153 
6.15663 


Ratio. 
65.886 
65.884 
65.883 

Mean,  65.884 


65.881 
65.883 
65.887 
65.882 


Mean,  65.883 
Mean  of  all  as  one  series,  65.884,  ±  .0006 

For  the  atomic  weight  of  strontium  we  now  have  the  subjoined  ratios 


(i.)  Ag2  :  SrCl2  :  :  100  :  73.4725,  ±  . 

(2.)  Ag2  :  SrCl2.6H2O  :  :  100  :  123.460,  dr  .0082 

(3.)  Per  cent.  H2O  in  SrCl2.6H2O,  40.573,  =b  .0033 

(4.)  SrCl2  :  SrSO4  :  :  100  :  115.936,  ±  .0040 

(5.)  Ag2  :  SrBr2  :  :  100  :  114.689,  H=  .0012 

(6.)  2  AgBr  :  SrBr2  :  :  100  :  65.884,  ±  .0006 


The  antecedent  values  are — 

O.  =  15.879,  ±  .0003 
Ag—  107.108,  ±  .0031 
Ci  =  35.179,  ±.0048 


Br       =    79-344,  ±.0062 
S  :    31.828,  db  .0015 

AgBr—  186.452,  ±  .0054 


STRONTIUM.  117 

For  the  molecular  weight  of  SrCl2  three  estimates  are  available  : 

From  (i) SrCI2  —  157.390,  =}=  .0112 

From  (2) "      =  157.197,  ±  .0192 

From  (3).... "      =  157-123,  ±  .°'57 

General  mean SrCl2  =  157.281,  ±  .0083 

For  SrBr2  there  are  two  values : 

From  (5) SrBr2  =  245.682,  ±  .0076 

From  (6) "      =  245.684,  rb  .0075 


General  mean SrBr2  =  245.683,  ±  .0053 

Finally,  with  these  intermediate  data  we  obtain  three  independent 
measures  of  the  atomic  weight  of  strontium,  as  follows : 

From  molecular  weight  SrCl2 Sr  =  86.923,  ±  .0127 

From  molecular  weight  SrBr2 "  =  86.995,  =t  -OI35 

From  ratio  (4) "  =  86.434,  ±  .081 1 


General  mean Sr  =  86.948,  ±  .0092 

If  0  =  16,  Sr  =  87.610.  Rejection  of  the  third  value,  which  is  worth- 
less, raises  these  means  by  0.01  only.  The  second  value,  86.995,  which 
represents  Richards'  work,  is  undoubtedly  the  best  of  the  three. 


118  THE    ATOMIC   WEIGHTS. 


BARIUM. 

For  the  atomic  weight  of  barium  we  have  a  series  of  eight  ratios,  estab- 
lished by  the  labors  of  Berzelius,  Turner,  Struve,  Marignac,  Dumas,  and 
Richards.  Andrews*  and  Salvetat,f  in  their  papers  upon  this  subject, 
gave  no  details  nor  weighings,  and  therefore  their  work  may  be  properly 
disregarded.  First  in  order,  we  may  consider  the  ratio  between  silver 
and  barium  chloride,  as  determined  by  Pelouze,  Marignac,  Dumas,  and 
Richards. 

Pelouze,  J  in  1845,  made  the  three  subjoined  estimations  of  this  ratio, 
using  his  well  known  volumetric  method.  A  quantity  of  pure  silver  was 
dissolved  in  nitric  acid,  and  the  amount  of  barium  chloride  needed  to 
precipitate  it  was  carefully  ascertained.  In  the  last  column  I  give  the 
quantity  of  barium  chloride  proportional  to  100  parts  of  silver: 

3.860  grin.  BaCl2  ppt.  4.002  grm.  Ag.  96.452 

5.790  "  6.003        "  96-452 

2.895  "  3-Qoi       "  96.468 


Mean,  96.4573,  ±  .0036 

Essentially  the  same  method  was  adopted  by  Marignac  §  in  1848.  His 
experiments  were  made  upon  four  samples  of  barium  chloride,  as  fol- 
lows. A,  commercial  barium  chloride,  purified  by  recrystallization  from 
water.  B,  the  same  salt,  calcined,  redissolved  in  water,  the  solution 
saturated  with  carbonic  acid,  filtered,  and  allowed  to  crystallize.  C,  the 
preceding  salt,  washed  with  alcohol,  and  again  recrystallized,  D,  the 
same,  again  washed  with  alcohol.  For  100  parts  of  silver  the  following 
quantities  of  chloride  were  required,  as  given  in  the  third  column  : 

Ag.  BaCL.  Ratio. 


(  3-4445 

3-3190 

96.356 

) 

A. 

\  3.748o 

3.6110 

96.345 

\  Mean,  96.354 

(6.3446 

6.1140 

96.362 

) 

|  4.3660 

4.1780 

96.356 

| 

B. 

{  4-8390 

4.6625   . 

96.352 

1  Mean,  96.354 

j  6.9200 

6.6680 

96.358 

~j 

C. 

{  5.6230 

5-4185 

96.363 

f-  Mean,  96.360 

(  5-8435 

5.6300 

96.346 

1 

1  8.5750 

8.2650 

96.384 

1 

. 

)  4.8225 

4.6470 

96.361 

[ 

[6.8460 

6.5980 

96.377 

J 

Mean,  96.360 

,  ±  .0024 

*  Chemical  Gazette,  October,  1852. 

fCompt.  Rend.,  17,  318. 

I  Compt.  Rend.,  20,  1047.     Journ.  fur  Prakt.  Chern.,  35,  73. 

g  Arch,  d.  Sci.  Phys.  etNat.,  8,  271. 


BARIUM. 


119 


Dumas*  employed  barium  chloride  prepared  from  pure  barium 
nitrate,  and  took  the  extra  precaution  of  fusing  the  salt  at  a  red  heat  in 
a  current  of  dry  hydrochloric  acid  gas.  Three  series  of  experiments 
upon  three  samples  of  chloride  gave  the  following  results  : 


L7585 
3.8420 
2.1585 
4.0162 
1.6625 
2.4987 
3.4468 
4.0822 
4.2062 
4.4564 
8.6975 
2.2957 
4.I372 
4.2662 

4.4764 
5.6397 


Ratio. 

96-303  1 

96.339  [ 

96.340  | 
96.358  j 
96.265^ 

96-304 

96.306 

96.290 

96.289 

96.271 

96.307 

96.3l6>| 

96.371 

96.303  \ 

96.329 
96-372J 


Mean,  96.333 


>.   Mean,  96.290 


Mean,  96.338 


Mean,  96.316,  dr  .0055 


The  work  done  by  Richards  f  was  of  a  much  more  elaborate  kind,  for 
it  involved  some  collateral  investigations  as  to  the  effect  of  heat  upon 
barium  chloride,  etc.  Every  precaution  was  taken  to  secure  the  spectro- 
scopic  purity  of  the  material,  which  was  prepared  from  several  sources, 
and  similar  care  was  taken  with  regard  to  the  silver.  For  details  upon 
these  points  the  original  paper  must  be  consulted.  As  for  the  titrations, 
three  methods  were  adopted,  and  a  special  study  was  made  with  refer- 
ence to  the  accurate  determination  of  the  end  point  ;  in  which  particular 
the  investigations  of  Pelouze,  Marignac,  and  Dumas  were  at  fault.  In  the 
first  series  of  determinations,  silver  was  added  in  excess,  and  the  latter 
was  measured  with  a  standard  solution  of  hydrochloric  acid.  The  end 
point  was  ascertained  by  titrating  backward  and  forward  with  silver 
solution  and  acid,  and  was  taken  as  the  mean  between  the  two  apparent 
end  points  thus  observed.  The  results  of  this  series,  with  weights  reduced 
to  vacuum  standards,  were  as  follows  : 


•AS- 

Bad,. 

Ratio. 

6.1872 

5.9717 

96.517 

5.6580 

5-4597 

96.495 

3-5988 

3.4728 

96.499 

9.4010 

9.0726 

96.507 

.7199 

.6950 

96.541 

Mean,  96.512,  d= 

•0055 

*Ann.  Chem. 

Pharm.,  113,  22.     1860.    Ann.  Chim. 

Phys.  (3),  55,  129. 

120  THE    ATOMIC    WEIGHTS. 

In  the  second  series  of  experiments  a  small  excess  of  silver  was  added 
as  before,  and  the  precipitate  of  silver  chloride  was  removed  by  filtra- 
tion. The  filtrate  and  wash  waters  were  concentrated  to  small  bulk 
whereupon  a  trace  of  silver  chloride  was  obtained  and  taken  into  account. 
The  excess  of  silver  remaining  was  then  thrown  down  as  silver  bromide, 
and  from  the  weight  of  the  latter  the  silver  was  calculated,  and  sub- 
tracted from  the  original  amount. 

Ag.  BaClT  Ratio. 

6.59993  6.36974  96.512 

5-55229  5-36oi°  96.539 

4.06380  3.92244  96.522  • 


Mean,  96.524,  ±  .0054 

The  third  series  involved  mixing  solutions  of  barium  chloride  and 
silver  in  as  nearly  as  possible  equivalent  amounts,  and  then  determining 
the  actual  quantities  of  silver  and  chlorine  left  unprecipitated.  The 
filtrate  and  wash  waters  were  divided  into  two  portions,  one-half  being 
evaporated  with  hydrobromic  acid  and  the  other  with  silver  nitrate. 
The  small  amounts  of  silver  bromide  and  chloride  thus  obtained  were 
determined  by  reduction  and  the  use  of  Volhard's  method  : 

Ag.  BaClv  Ratio. 

4-4355  4.2815  96.528 

2.7440  2.6488  96.531 

6.1865  5-9712  96.520 

3  4023  3.2841  96.526 


Mean,  96.526,  ±  .0035 

Two  final  experiments  were  carried  out  by  Stas'  method,  somewhat  as 
in  the  first  series,  with  variations  and  greater  refinement  in  the  observa- 
tion of  the  end  point.  The  results  were  as  follows  : 

Ag.  Bad*.  Ratio. 

6.7342  6.50022  96.525 

10.6023  IO-23365  96.523 


Mean,  96.524,  ±  .0007 

A  careful  study  of  Richards'  paper  will  show  that,  although  the  last 
two  experiments  are  probably  the  best,  they  are  not  entitled  to  such  pre- 
ponderance of  weight  as  the  "  probable  error"  here  computed  would 
give  them.  I  therefore  treat  Richards'  work  as  I  have  already  done  that 
of  Marignac  and  Dumas,  regarding  all  of  his  series  as  one,  which  gives  for 
the  value  of  the  ratio  96.520,  ±  .0025.  This  combines  with  the  previous 
series  thus : 


BARIUM.  121 

Pelouze 96.457,  rfc  .0036 

Marignac 96.360,  ±  .0024 

Dumas 96.316,  db  .0055 

Richards 96.520,  ±  .0025 


General  mean  ....................    96.434,  ±  .0015 

The  ratio  between  silver  and  crystallized  barium  chloride  has  also 
been  fixed  by  Marignac.*  The  usual  method  was  employed,  and  two 
series  of  experiments  were  made,  in  the  second  of  which  the  water  of  crys- 
tallization was  determined  previous  to  the  estimation.  Five  grammes  of 
chloride  were  taken  in  each  determination.  The  following  quantities  of 
BaCl7.2H2O  correspond  to  100  parts  of  silver  : 

113.109") 
A.  J  113.135  V  Mean,  113.114 


- 

B.  J  113.122  V-  Mean,  113.106 
(113.060) 

Mean,  113.110,  ±  .0079 

The  direct  ratio  between  the  chlorides  of  silver  and  barium  has  been 
measured  by  Berzelius.  Turner,  and  Richards.  Berzelius  t  found  of 
barium  chloride  proportional  to  100  parts  of  silver  chloride  — 

72.432 
72.422 


Mean,  72.427 

Turner  J  made  five  experiments,  with  the  following  results  : 

72.754 
72.406 
72.622 
72.664 
72.653 


Mean,  72.680,  ±  .0154 

Of  these,  Turner  regards  the  fourth  and  fifth  as  the  best ;  but  for 
present  purposes  it  is  not  desirable  to  so  discriminate. 

Richards'  determinations  §  fall  into  three  series,  and  all  are  character- 
ized by  their  taking  into  account  chloride  of  silver  recovered  from  the 
wash  waters.  In  the  first  series  the  barium  chloride  was  ignited  at  low 
redness  in  air  or  nitrogen  ;  in  the  second  series  it  was  fused  in  a  stream 
of  pure  hydrochloric  acid  ;  and  in  the  third  series  it  was  not  ignited  at 
all.  In  the  last  series  it  was  weighed  in  the  crystallized  state,  and  the 

*  Tourn.  fur  Prakt.  Chem.,  74,  212.     1858. 

t  Poggend.  Annalen,  8,  177. 

t  Phil.  Trans.,  1829,  291. 

\  Proc.  Amer.  Acad.,  29,  55,  1893. 


122  THE    ATOMIC   WEIGHTS. 

amount  of  anhydrous  chloride  was  computed  from  the  data  so  obtained. 
The  data,  corrected  to  vacuum  standards,  are  as  follows : 

AgCl.  Bad*.  Ratio. 

(  8.7673  6.3697  72.653    •} 

I  5-1979  3.7765  72.654 

A.  1  4.9342  3.5846  72.648     ^  Mean,  72.649 

|  2.0765  1.5085  72.646     | 

U-427I  3.2163  72.650    J 

2.09750  1.52384  72-650   ^ 

B.  ^7.37610  5.36010  72.669     V-  Mean,  72.6563 

5.39906  3-92244  72.650    ) 

8.2189  5.97123  72.6524 1 

4.5199  3.28410  72.6587}   P     an'72-' 


Mean,  72.653,  ±  .0014 

If  we  assign  Berzelius'  work  equal  weight  with  that  of  Turner,  the 
three  series  representing  the  ratio  2AgCl  :  BaCl2  combine  as  follows  • 

Berzelius 72.427,  =b  .01 54 

Turner 72.680,  ±  .0154 

Richards 72.653,  ±  .0014 


General  mean 72.650,  i  .0014 

Incidentally  to  some  of  his  other  work,  Marignac*  determined  the 
percentage  of  water  in  crystallized  barium  chloride.  Two  sets  of  three 
experiments  each  were  made,  the  first  upon  five  grammes  and  the  socond 
upon  ten  grammes  of  salt.  The  following  are  the  percentages  obtained  : 

f  14.79*0 

A.  J  14.796  y  Mean,  14.795 
(14.800) 

c  14.80  S 

.       B.  1  14.81     C  Mean,  14.803 
(14-80    ) 

Mean,  14.799,  —  .0018 

The  ratio  between  barium  nitrate  and  barium  sulphate  has  been  de- 
termined only  by  Turner,  f  According  to  his  experiments  100  parts  of 
sulphate  correspond  to  the  following  quantities  of  nitrate : 

112.060 
111.990 
112.035 


Mean,  112.028,  ±  .014 

For  the  similar  ratio  between  barium  chloride  and  barium  sulphate, 
there  are  available  determinations  by  Turner,  Berzelius,  Struve,  Marignac, 
and  Richards. 


*  Journ.  fur  Prakt.  Chem.,  74,  312.     1858. 
fPhil.  Trans.,  1833.  538. 


BARIUM.  123 

Turner  *  found  that  100  parts  of  chloride  ignited  with  sulphuric  acid 
gave  112.19  parts  of  sulphate.  By  the  common  method  of  precipitation 
and  nitration  a  lower  figure  was  obtained,  because  of  the  slight  solubility 
of  the  sulphate.  This  point  bears  directly  upon  many  other  atomic 
weight  determinations. 

Berzelius,f  treating  barium  chloride  with  sulphuric  acid,  obtained 
the  following  results  in  BaS04  for  100  parts  of  BaCl2 : 

112.17 
112.18 


Mean,  112.175 

Struve,  I  in  two  experiments,  found  : 

112.0912 
112.0964 

Mean,  1  12.0938 

Marignac's§  three  results  are  as  follows  : 

8.520  grm.  BaCI2  gave  9.543  BaSO4.  Ratio,  112.007 

8.519  9.544      "  "       112.032 

8.520  "  9-542      "  "      ui-995 


Mean,  112.011,  ±  .0071 

Richards,  in  his  work  on  this  ratio,  regards  the  results  as  of  slight 
value,  because  of  the  occlusion  of  the  chloride  by  the  sulphate.  This 
source  of  error  he  was  never  able  to  avoid  entirely.  Another  error  in 
the  opposite  direction  is  found  in  the  retention  of  sulphuric  acid  b}r  the 
precipitated  sulphate.  Eight  experiments  were  made  in  two  series,  one 
set  by  adding  sulphuric  acid  to  a  strong  solution  of  barium  chloride  in  a 
platinum  crucible,  the  other  by  precipitation  in  the  usual  way.  Rich- 
ards gives  in  his  published  paper  only  the  end  results  and  the  mean  of 
his  determinations  ;  the  details  cited  below  I  owe  to  his  personal  kind- 
ness. The  weights  are  reduced  to  vacuum  standards  : 

Bad.,.  BaSO*  Ratio. 

1.78934  2.0056  112.086 

2.07670  2.3274  112.072 

1.58311  i.774i  112.064 

3.27563  3-67i2  112.076 

3.02489  3-39°3  112.080 

3.87091  4.3385  112.080 

(3.02489  3-9726  112.076 

nd-    (3,87091  3.4880  112.085 

Mean,  112.077,  ±  .0017 

*  Phil.  Trans.,  1829,  291. 

t  Poggend.  Annalen,  8,  177. 

1  Ann.  Cheni.  Pharm.,  80,  204.     1851. 

g  Journ.  fi'ir  Prakt.  Chem.,  74,  212.     1858. 


First. 


124  THE    ATOMIC    WEIGHTS. 

This  mean  is  subject  to  a  small  correction  due  to  loss  of  chlorine  on 
drying  the  chloride,  which  reduces  it  to  112.073.  Omitting  Turner's 
single  determination  as  unimportant,  and  assigning  to  the  work  of  Ber- 
zelius  and  of  Struve  equal  weight  with  that  of  Marignac,  the  measure- 
ments of  this  ratio  combine  thus : 

Berzelius 112.175,  =t  .0071 

Struve ii  2.094,  =t  .°°7 r 

Marignac... 112.011,^.0071 

Richards 1 12.073,  ±  .0017 


General  mean 112.075,  ±  .0016 

In  an  earlier  paper  than  the  one  previously  cited,  Richards*  studied 
with  great  care  the  ratios  connecting  barium  bromide  with  silver  and 
silver  bromide.  The  barium  bromide  was  prepared  by  several  distinct 
processes,  its  behavior  upon  dehydration  and  even  upon  fusion'was 
studied,  and  its  specific  gravity  was  determined.  The  ratio  with  silver 
was  measured  by  titration,  a  solution  of  hydrobromic  acid  being  used 
for  titrating  back.  The  data  are  subjoined,  with  the  BaBr2  equivalent 
to  100  parts  of  silver  stated : 

BaBrT  Ag.  Ratio. 

2.28760  1.66074  137.746 

3.47120  2.52019  I37-736 

2.19940  1.59687  I37.732 

2-3597i  i.7'323  '37-735 

2.94207  2.13584  137-748 

1.61191  1.17020  137.747 

2.10633  i.5292i  137.740 

2.19682  2.11740  137.755 

237290  1.72276  137.738 

1.84822  L34I75  137.747 

5.66647  4.11360  I37.750 

3.52670  2.56010  »37.756 

4-3l690  3-I343°  I37-731 

3-36635  2.44385  137.748 

3.46347  2.51415  137-759 


Mean,  137.745,  ±  .0015 

The  silver  bromide  in  most  of  these  determinations,  and  in  some  others, 
was  collected  and  weighed  in  a  Gooch  crucible  with  all  necessary  pre- 
cautions. Vacuum  standards  were  used  throughout  for  both  ratios.  I 
give  in  a  third  column  the  BaBr2  equivalent  to  100  parts  of  AgBr : 

§  Proc.  Amer.  Acad.,  28.     1893. 


BARIUM.  125 

AgBr.  Ratio. 

2.28760  2.89026  79-149 

3-47120  4.3*635  79.136 

3.81086  4.81688  79.133 

2.35971  2.98230  79-124 

2.94207  3-71809  79-129 

2.10633  2.66191  79.128 

2.91682  3.68615  79.129 

2.37290  2.99868  79.131 

1.84822  2.33530  79.143 

1.90460  2.40733  79.116 

5.66647  7.16120  79.127 

3.52670  4.45670  79-133 

2.87743  3-63644  79-127 

3.46347  4-37669  79.135 

Mean,  79.132,  ±  .0015 
The  ratios  for  barium  now  sum  up  as  follows: 

(I.)  Ag2  :  BaC)2  :  :  100  :  96.434,  ±  .0015 

(2.)  Ag2  :  BaCl2.2H2O  :  :  100  :  113.110,  ±  .0079 

(3.)  2AgCl  :  BaG2  :  :  100  :  72.650,  =fc  .0014 

(4.)  Per  cent,  of  H2O  in  BaCl2.2H2O,  14.799,  =b  .0018 

(5.)  BaSO4  :  BaN2O6  :  :  100  :  112.028,  ±  .014 

(6.)  BaCl2  :  BaSO4  :  :  100  :  112.075,  =h  .0016 

(7.)  Ag2  :  BaBr2  :  :  100  :  137-745,  ±  .0015 

(8.)  2AgBr  :  BaBr2  :  :  100  :  79.132,  ±  .0015 

The  reduction  of  these  ratios  depends  upon  the  subjoined  antecedent 
values : 

Ag=  107.108,  ±  .0031  N    =  13.935,  =b  .0021 

Cl  =  35.179,^.0048  S    ==  31.828,  ±  .0015 

Br  =  79.344,  ±  .0062  AgCl  =  142.287,  dz  .0037 

O  =  15.879,  ±  .0003  AgBr  =  186.452,  ±  .0054 

With  these  factors  four  estimates  are  obtainable  for  the  molecular 
weight  of  barium  chloride  : 

From  (i) BaCl2  =  206.577,  ±  .0068 

From  (2) "       =  206.542,  ±  .0183 

From  (3) "      —  206.745,  ±  .0067 

From  (4) "      =  205.866,  ±  .0257 

General  mean BaCl2  =  206.629,  ±  .0045 

For  barium  bromide  we  have : 

From  (7) BaBr2  —  295.070,  ±  .0091 

From  (8) "      =295.086,^.0102 


General  mean BaBr2  =  295.078,  ±  .0068 


126  THE    ATOMIC    WEIGHTS. 

And  for  barium  itself,  four  values  are  finally  available,  thus  : 

From  molecular  weight  BaCl2 Ba  =  136.271,  ±  .0106 

From  molecular  weight  BaBr.2 "  =  136.390,  ±  .0141 

From  ratio  (5) "  —  135.600,  rb  .2711 

From  ratio  (6) "  =  136.563,  ±  .0946 


General  mean Ba  =  136.315,  d=  .0085 

Or,  if  0  =  16,  Ba  =  137.354. 

In  the  foregoing  computation  all  the  data,  good  or  bad,  are  included. 
Some  of  them,  as  shown -by  the  weights,  practically  vanish ;  but  others, 
as  in  the  chloride  series,  carry  an  undue  influence.  A  more  trustworthy 
result  can  be  deduced  from  Richards'  experiments  alone,  which  reduce 
as  follows : 

From  Ag2  :  BaCl2 BaCl2  =  206.761,  ±  .0080 

From  2AgCl  :  BaCl2 "      =  206.754,  ±  .0067 


General  mean BaCl2  =  206.755, 

From  the  bromide,  as  given  above,  Ba  =  136.390,  dz  .0141.  From  the 
value  just  found  for  the  chloride,  Ba  —  136.397,  ±  .0109.  Combining 
the  two  values — 

Ba  =  136.392,  ±  .0086. 

Or,  if  0  =  16,  Ba  =  137.434.  This  determination  will  be  adopted  in 
subsequent  calculations  as  the  most  probable. 


LEAD.  127 


LEAD. 

For  the  atomic  weight  of  lead  we  have  to  consider  experiments  made 
upon  the  oxide,  chloride,  nitrate,  and  sulphate.  The  researches  of  Ber- 
zelius  upon  the  carbonate  and  various  organic  salts  need  not  now  be 
considered,  nor  is  it  worth  while  to  take  into  account  any  work  of  his 
done  before  the  year  1818.  The  results  obtained  by  Dobereiner*  and 
by  Longchamp  f  are  also  without  special  present  value. 

For  the  exact  composition  of  lead  oxide  we  have  to  depend  upon  the 
researches  of  Berzelius.  His  experiments  were  made  at  different  times 
through  quite  a  number  of  years  ;  but  were  finally  summed  up  in  the 
last  edition  of  his  famous  *'  Lehrbuch."  J  In  general  terms  his  method 
of  experiment  was  very  simple.  Perfectly  pure  lead  oxide  was  heated 
in  a  current  of  hydrogen,  and  the  reduced  metal  weighed.  From  his 
weighings  I  have  calculated  the  percentages  of  lead  thus  found  and 
given  them  in  a  third  column  : 

Earlier  Results. 

8.045  grm-  PbO  Save    74675  grm.  Pb.  92.8217  per  cent. 

14.183  "  13.165         "  92.8224       " 

10.8645  "  10.084         "  92.8160       " 

13.1465  "  12.2045        "  92.8346       " 

21.9425  "  20.3695       "  92.8313       " 

11.159  "  IO-359        "  92.8309      " 

Latest. 

6.6155  6.141         "  92.8275       " 

14.487  "  13.448        "  92.8280      " 

14.626  <(  13-5775       "  92.8313       " 


Mean,  92.8271,  ±  .0013 

For  the  synthesis  of  lead  sulphate  we  have  data  by  Berzelius,  Turner, 
and  Stas.  Berzelius,  §  whose  experiments  were  intended  rather  to  fix 
the  atomic  weight  of  sulphur,  dissolved  in  each  estimation  ten  grammes 
of  pure  lead  in  nitric  acid,  then  treated  the  resulting  nitrate  with  sul- 
phuric acid,  brought  the  sulphate  thus  formed  to  dryness,  and  weighed. 
One  hundred  parts  of  metal  yield  of  PbS04 : 

146.380 
146.400 
146.440 
146.458 

Mean,  146.419,  ±  .012 

*  Schweig.  Journ.,  17,  241.     1816. 
f  Ann.  Chim.  Phys.,  34,  105.     1827. 
t  Bd.  3,  s.  1218. 
I  I^ehrbuch,  sth  ed.,  3,  1187. 


128  THE    ATOMIC    WEIGHTS, 

Turner,*  in  three  similar  experiments,  found  as  follows  : 

146.430 
146.398 
146.375 


Mean,  146.401,  ±  .on 

In  these  results  of  Tamer's,  absolute  weights  are  implied. 
The  results  of  Stas'  syntheses,t  effected  after  the  same  general  method, 
but  with  variations  in  details,  are  as  follows.     Corrections  for  weighing 
in  air  were  applied  : 

146.443 

146.427 

146.419 

146.432 

146.421 

146.423 

Mean,  146.4275,  ±  .0024 

Combining,  we  get  the  subjoined  result: 

Berzelius 146.419,    ±.012 

Turner 146.401,    ±  .01 1 

Stas 146.4275,  ±  .0024 


General  mean 146.4262,  ±  .0023 

Turner,  in  the  same  paper,  also  gives  a  series  of  syntheses  of  lead  sul- 
phate, in  which  he  starts  from  the  oxide  instead  of  from  the  metal.  One 
hundred  parts  of  PbO,  upon  conversion  into  PbS04,  gained  weight  as 
follows : 

35-84 

35-71 

35.84 

35-75 

35-79 

35.78 

35.92 

Mean,  35.804,  ±  .018 

These  figures  are  not  wholly  reliable.  Numbers  one,  two,  and  three 
represent  lead  oxide  contaminated  with  traces  of  nitrate.  The  oxide  of 
four,  five,  and  six  contained  traces  of  minium.  Number  seven  was  free 
from  these  sources  of  error,  and,  therefore,  deserves  more  consideration. 
The  series  as  a  whole  undoubtedly  gives  too  low  a  figure,  and  this  error 
would  tend  to  slightly  raise  the  atomic  weight  of  lead. 

*Phil.  Trans.,  1833,  527-538. 
t  Aronstein's  translation,  333. 


LEAD.  129 

Still  a  third  series  by  Turner  establishes  the  ratio  between  the  nitrate 
and  the  sulphate,  a  known  weight  of  the  former  being  in  each  experi- 
ment converted  into  the  latter.  One  hundred  parts  of  sulphate  represent 

of  nitrate: 

109.312 
109.310 
109.300 


Mean,  109.307,  ±  .002 

In  all  these  experiments  by  Turner  the  necessary  corrections  were 
made  for  weighing  in  air. 

In  1846  Marignac*  published  two  sets  of  determinations  of  only 
moderate  value.  First,  chlorine  was  conducted  over  weighed  lead,  and 
the  amount  of  chloride  so  formed  was  determined.  The  lead  chloride 
was  fused  before  weighing.  The  ratio  to  100  Pb  is  given  in  the  last 
column : 

20.506  grm.  Pl>  gave  27.517  PbCl2.  134.190 

16.281  "  21.858     "  134.225 

25.454  34.H9     "  '34.159 

Mean,  134.19^  ±  .013 

Secondly,  lead  chloride  was  precipitated  by  silver  nitrate  and  the  ratio 
between  PbCl,  and  2AgCl  determined.  The  third  column  gives  the  AgCl 
formed  by  100  parts  of  PbCl2 : 

12.534  grm.  PbCl2  gave  12.911  AgCl.  103.01 

14.052  14.506       "  JO3.23 

25.533  "  26.399       "  103.39 

Mean,  103.21,  ±  .0745 

For  the  ratio  between  lead  chloride  and  silver  we  have  a  series  of  re- 
sults by  Marignac  and  one  experiment  by  Dumas.  There  are  also  un- 
available data  by  Turner  and  by  Berzelius. 

Marignac,t  applying  the  method  used  in  his  researches  upon  barium 
and  strontium,  and  working  with  lead  chloride  which  had  been  dried  at 
200°,  obtained  these  results.  The  third  column  gives  the  ratio  between 
PbCl2,  and  100  parts  of  Ag: 

4.9975  grm.  PbCl2  =  3.8810  grm.  Ag.  128.768 

4.9980  "  3.8835          "  128.698 

5.0000  3.8835          "  128.750 

5.0000  "  3.8860          "  128.667 

Mean,  128.721,  ±  .016 

Dumas, J  in  his  investigations,  found  that  lead  chloride  retains  traces 

*Aun.  Chern.  Pharrn.,  59,  289;  and  290.     1846. 
t  Journ.  fiir  Prakt.  Chem.,  74,  218.     1858. 
I  Ann.  Chem.  Pharm.,  113,  35.     1860. 


130  THE    ATOMIC    WEIGHTS. 

of  water  even  at  250°,  and  is  sometimes  also  contaminated  with  oxychlo- 
ride.  In  one  estimation  8.700  grammes  PbCl2  saturated  6.750  of  Ag. 
The  chloride  contained  .009  of  impurity  ;  hence,  correcting,  Ag  :  PbCI2  :  : 
100  :  128.750.  If  we  assign  this  figure  equal  weight  with  those  of  Marig- 
nac,  we  get  as  the  mean  of  all  128.7266,  ±  .013.  The  sources  of  error  in- 
dicated by  Dumas,  if  they  are  really  involved  in  this  mean,  would  tend 
slightly  to  raise  the  atomic  weight  of  lead. 

The  synthesis  of  lead  nitrate,  as  carried  out  by  Stas,*  gives  excellent 
results.  Two  series  of  experiments  were  made,  with  from  103  to  2pO 
grammes  of  lead  in  each  determination.  The  metal  was  dissolved  in 
nitric  acid,  the  solution  evaporated  to  dryness  with  extreme  care,  and 
the  nitrate  weighed.  All  weighings  were  reduced  to  the  vacuum  standard. 
In  series  A  the  lead  nitrate  was  dried  in  an  air  current  at  a  temperature 
of  about  155.°  In  series  B  the  drying  was  effected  in  vacuo,  100  of  lead 
yield  of  nitrate  : 

A. 

159-973 
159.975 

159.982 

159-975 
159.968 

J59-973 
Mean,  159.9743,  =fc  .0012 


159.970 
159.964 
159-959 
I59-965 

Mean,  159.9645,  ±  .0015 
Mean  from  both  series,  159.9704,  ±2  .0010 

There  is  still  another  set  of  experiments  upon  lead  nitrate,  originally 
intended  to  fix  the  atomic  weight  of  nitrogen,  which  may  properly  be 
included  here.  It  was  carried  out  by  Anderson  f  in  Svanberg's  labora- 
tory, and  has  also  appeared  under  Svanberg's  name.  Lead  nitrate  was 
carefully  ignited,  and  the  residual  oxide  weighed,  with  the  following 
results  : 

5.19485  grm.  PbN2O6  gave  3.5017  grm.  PbO.  67.4071  per  cent. 

9.7244  6.5546         "  67.4037        " 

9.2181  6.2134          "  67.4044       " 

9.6530  6.5057          "  67.3957 

Mean,  67.4027,  i  .0016 

*  Aronsteiii's  translation,  316. 

t  Ann.  Chim.  Phys.  (3),  9,  254.     1843. 


LEAD.  131 

We  have  now  nine  ratios  from  which  to  compute : 

(i.)   Per  cent,  of  Pb  in  PbO,  92.8271,  ±  .0013 
(2.)   Per  cent  of  PbO  in  PbN2O6,  67.4027,  ±  .0016 
(3.)   Pb  :  PbSO4  :  :  100  :  146.4262,  ±  .0023 
(4.)   PbO  :  PbSO4  :  :  100  :  135.804,  ±  .0180 
(5.)   PbSO4  :  PbN2O6  :  :  100  :  109.307,  ±  .0020 
(6.)   Pb  :  PbN2O6  :  :  iqo  :  159.9704,  ±  .0010 
(7.)   Pb  :  PbC)2  :  :  100  :  134.191,  ±  .013 
(8.)   PbCl2  :  2AgCl  :  :  100  :  103.21,  ±  .0745 
(9.)  Ag2  :  PbCl2  :  :  100  :  128.7266,  db  .0130 

To  reduce  these  ratios  we  must  use  the  following  data : 

O   =.   15.879,  ±  .0003  s       =  31.828,  ±  .0015 

Ag=  107.108,  =b  .0031  N       —    13.935,^.0021 

Cl  ==    35.179,  db  .0048  AgCl=  142.287,  ±.0037 

For  the  molecular  weight  of  lead  oxide  we  now  get  three  estimates  : 

From  (i) PbO  =  221.375,  d=  .0403 

From  (2) "     —  221.796,  ±  .0132 

From  (4) "     =  221.944,  d=  .1116 


General  mean PbO  =  221.757,  =b  .0125 

For  lead  chloride  we  have — 

From  (8) PbCl2  =  275.723,  ±  .1989 

From  (9) "      =  275.753,^.0290 

General  mean PbO2  =  275.752,  dr  .0287 

Including  these  results,  six  values  are  calculable  for  the  atomic  weight 
of  lead : 

From  molecular  weight  of  PbO Pb  =  205.878,  dr  .0126 

From  molecular  weight  of  PbCl2 "    =  205.394,  ±  .0302 

From  (3) "    =  205.367,  dr  .0051 

From  (5) "   =  203.352,  ±  .0479 

From  (6) "    =  205.341,  db  .0068 

From  (7) "    =  205.779,  ±  .0831 


General  mean Pb  =  205.395,  ±  .0038 

If  0  =  16,  Pb  =  206.960.  If  we  reject  the  first,  fourth,  and  sixth  of 
these  values,  which  are  untrustworthy,  the  remaining  second,  third,  and 
fifth  give  a  general  mean  of  Pb  =  205.358,  ±  .0040.  If  O  =  16,  this 
becomes  Pb  =  206.923.  From  Stas'  ratios  alone  Stas  calculates  Pb  = 
206.918  to  206.934 ;  Ostwald  finds  206.911 ;  Van  der  Plaats  (A),  206.9089, 
(B),  206.9308,  and  Thomson  206.9042.  The  value  adopted  here  repre- 
sents mainly  the  work  of  Stas,  and  with  H  =  1  is 

Pb  =  205.358,  ±  .0040. 


132  THE   ATOMIC    WEIGHTS. 

GLUCINUM. 

Our  knowledge  of  the  atomic  weight  of  glucinum  is  chiefly  derived 
from  experiments  made  upon  the  sulphate.  Leaving  out  of  account  the 
single  determination  by  Berzelius,  *  we  have  to  consider  the  data  fur- 
nished by  Awdejew,  Weeren,  Klatzo,  Debray,  Nilson  and  Pettersson,  and 
Kriiss  and  Moraht. 

Awdejew,  f  whose  determination  was  the  earliest  of  any  value,  analyzed 
the  sulphate.  The  sulphuric  acid  was  thrown  down  as  barium  sulphate  ; 
and  in  the  nitrate,  from  which  the  excess  of  barium  had  been  first  re- 
moved, the  glucina  was  precipitated  by  ammonia.  The  figures  which 
Awdejew  publishes  represent  the  ratio  between  S03  and  G10,  but  not 
absolute  weights.  As,  however,  his  calculations  were  made  with  S03  = 
501.165,  and  Ba  probably  —  855.29,  we  may  add  a  third  column  showing 
how  much  BaS04  is  proportional  to  100  parts  of  G10  : 

SOS.  GIO.  Ratio. 


4457  !4o  921.242 

4531  1420  927.304 

7816  2480  9I5-9°3 

12880  4065  920  814 


Mean,  921.316,  ±  LS77 

The  same  method  was  followed  by  Weeren  and  by  Klatzo,  except  that 
Weeren  used  ammonium  sulphide  instead  of  ammonia  for  the  precipita- 
tion of  the  glucina.  Weeren  J  gives  the  following  weights  of  GIO  and 
BaS04.  The  ratio  is  given  in  a  third  column,  just  as  with  the  figures  by 
Awdejew  : 

GIO.  BaSO±.  Ratio. 

.3163  2.9332  927.031 

.2872  2.6377  918  419 

.2954  2.7342  925-592 

.5284  4.8823  902.946 


Mean,  918.497,  =b  3.624 

Klatzo's  §  figures  are  as  follows,  with  the  third  column  added  by  the 

writer : 

GIO.  BaSO±.  Ratio. 

.2339  2.1520  920.052 

.1910  J-7556  919.162 

.2673  2.4872  930-49° 

•3585  3-3"5  923.7io 

.2800  2.5842  922.989 

Mean,  923.281,  ±  1.346 

*  Poggend.  Annal.,  8,  i. 

t  Poggend.  Aiinal.,  56,  106.     1842. 

t  Poggend.  Aiinal.,  92,  124.     1854. 

g  Zeitschr.  Anal.  Chem.,  8,  523.     1869. 


GLUCINUM.  133 

Combining  these  series  into  a  general  mean,  we  get  the  subjoined  result : 

Awdejew 921.316,  ±  L577 

Weeren 9l8-497,  ±  3.624 

Klatzo 923.281,  -_h  1.346 


General  mean 922.164,  dr  0.985 

Hence  G10  =  25.130,  ±  .0269. 

Debray*  analyzed  a  double  oxalate  of  glucinum  and  ammonium, 
G1(NH4)2C408.  In  this  the  glucina  was  estimated  by  calcination,  after 
first  converting  the  salt  into  nitrate.  The  following  percentages  were 
found : 

ii.5 

II. 2 

ii. 6 


Mean,  11.433,  d=  .081 

The  carbon  was  estimated  by  an  organic  combustion.     I  give  the 
weights,  and  put  in  a  third  column  the  percentages  of  CO2  thus  obtained  : 

Salt.                                  CO*  Per  cent.  COV 

.600                                   .477  79  500 

.603                                   .478  79.270 

.600                                   .477  79-5°° 


Mean,  79.423,  ±  .052 

Calculating  the  ratio  between  C02  and  G10,  we  have  for  the  molecular 
weight  of  the  latter,  G1O  =  25.151,  ±  .1783. 

In  1880  the  careful  determinations  of  Nilson  and  Pettersson  appeared.f 
These  chemists  first  attempted  to  work  with  the  sublimed  chloride  of 
glucinum,  but  abandoned  the  method  upon  finding  the  compound  to 
be  contaminated  with  traces  of  lime  derived  from  a  glass  tube.  They 
finally  resorted  to  the  crystallized  sulphate  as  the  most  available  salt 
for  their  purposes.  This  compound,  upon  strong  ignition,  yields  pure 
glucina.  The  data  are  as  follows : 

GISO^H.,O.  GIO.  Percent.  GIO. 

3-8014  .5387 

2.6092  -3697 

>  4. 307  2  .6099 

3.0091  .4266 

Mean,  14.169,  ±  .0023 

Kriiss  and  MorahtJ  in  their  work  follow  the  general  method  adopted 

*Ann.  Chim.  Phys.  ($\  44,  37-     l855- 

f  Berichte  d.  Deutsch.  Chem.  Gesell.,  13,  1451.     1880. 

J  Ann.  d.  Chem.,  262,  38.     1891. 


-  -_-_._v 


---: 
:-:.-: 

'  —  ; 


---  ;: 

-  -  '  ;- 

-55 


—  -':- 


-    •--- 


-    ' 


-    :    -     - 
- 


C  —  \\jyx 

. 


: 

- 

: 


=  -:     5      =      ~:: 


e 


I:   0=  1-     >-  -  -  ">•': 
« 
Tl 


:: ...  - 


:  •    .   --      :-:,-:.        . 


-" 


:,    :-; 

.,.    .,. 


136  THE    ATOMIC    WEIGHTS. 

In  a  later  note*  Scheerer  shows  that  the  barium  sulphate  of  these  ex- 
periments carries  down  with  it  magnesium  salts  in  such  quantity  as  to 
make  the  atomic  weight  of  magnesium  0.039  too  low. 

The  work  of  Bahr,  Jacquelain,  Macdonnell,  and  Marignac,  and  in  part 
that  of  Svanberg  and  Nordenfeldt,  also  relates  to  the  composition  of 
magnesium  sulphate. 

Jacquelain's  experiments  were  as  follows  :  f  Dry  magnesium  sulphate 
was  prepared  by  mixing  the  ordinary  hydrous  salt  to  a  paste  with  sul- 
phuric acid,  and  calcining  the  mass  in  a  platinum  crucible  over  a  spirit 
lamp  to  constant  weight  and  complete  neutrality  of  reaction.  This  dry 
sulphate  was  weighed  and  intensely  ignited  three  successive  times.  The 
weight  of  the  residual  MgO  having  been  determined,  it  was  moistened 
with  sulphuric  acid  and  recalcined  over  a  spirit  lamp,  thus  reproducing 
the  original  weight  of  MgS04.  Jacquelain's  weighings  for  these  two 
experiments  show  that  100  parts  of  MgO  correspond  to  the  quantities 
of  MgS04  given  in  the  last  column  : 

1.466  grm.  MgSO4  gave    .492  grm.  MgO.  297.968 

.492     "     MgO         "     1.466     "     MgSO4.  297.968 

Jacquelain  also  made  one  estimation  of  sulphuric  acid  in  the  foregoing 
sulphate  as  BaS04.  His  result  (1.464  grm.  MgS04  =  2.838  grm.  BaSOJ, 
reduced  to  the  standard  adopted  in  dealing  with  Scheerer's  experiments, 
gives  for  100  parts  of  MgS04, 193.852  BaS04.  If  this  figure  be  given  equal 
weight  with  a  single  experiment  in  Scheerer's  series,  and  combined  with 
the  latter,  the  mean  will  be  193.700,  ±  .0331.  This  again  is  subject  to 
the  correction  pointed  out  by  Scheerer  for  magnesium  salts  retained  by 
the  barium  sulphate,  but  such  a  correction  determined  by  Scheerer  for 
a  single  experiment  is  only  a  rough  approximation,  and  hardly  worth 
applying. 

The  determinations  published  by  Macdonnell  J  are  of  slight  impor- 
tance, and  all  depend  upon  magnesium  sulphate.  First,  the  crystallized 
salt,  MgS04.7H20,  was  dried  in  vacuo  over  sulphuric  acid  and  then  de- 
hydrated at  a  low  red  heat.  The  following  percentages  of  water  were 
found : 

5^7 

51.14 

51.26 
51.28 
5r-29 

Mean,  51.21,  ±  .020 

*Poggend.  Annalen,  70,  407. 

f  Ann.  Chim.  Phys.  (3),  32,  202. 

J  Proc.  Royal  Irish  Acad.,  5,  303.     British  Association  Report,  1852,  part  2,  p.  36. 


MAGNESIUM.  137 


Secondly,  anhydrous  magnesium  sulphate  was  precipitated  with  ba- 
rium chloride.  From  the  weight  of  the  barium  sulphate,  with  S03  = 
80  and  Ba  =  137,  Macdonnell  computes  the  percentages  of  S03  given 
below.  I  calculate  them  back  to  the  observed  ratio  in  uniformity  with 
Scheerer's  work : 


Per  cent.  SO,.  Ratio,  MgSO±  : 

66.67  194.177 

66.73  '94-351 

66.64  194.089 

66.65  194.118 
66.69  194-239 


In  another  experiment  60.05  grains  MgS04  gave  116.65  grains  BaS04, 
a  ratio  of  100  :  194.254.  Including  this  with  the  preceding  figures,  they 
give  a  mean  of  194.205,  ±  .027.  This,  combined  with  the  work  of 
Scheerer  and  Jacquelain,  193.700,  ±  .033,  gives  a  general  mean  of — 

MgSO4  :  BaSO4  :  :  100  :  194.003,  ±  .021. 

In  one  final  experiment  Macdonnell  found  that  41.44  grains  of  pure 
magnesia  gave  124.40  grains  of  MgSO4,  or  300.193  per  cent. 

Bahr's  *  work  resembles  in  part  that  of  Jacquelain.  This  chemist 
converted  pure  magnesium  oxide  into  sulphate,  and  from  the  increase 
in  weight  determined  the  composition  of  the  latter  salt.  From  his  weigh- 
ings 100  parts  of  MgO  equal  the  amounts  of  MgS04  given  in  the  third 
column : 

1.6938  grm.  MgO  gave  5.0157  grm.  MgSO4.  296.122 

2.0459  "  6.0648  "  296.437 

1.0784  "  3.I925  "  296.040 


Mean,  296.200,  d=  .0815 

About  four  years  previous  to  the  investigations  of  Bahr  the  paper  of 
Svanberg  and  Nordenfeldtf  appeared.  These  chemists  started  with  the 
oxalate  of  magnesium,  which  was  dried  at  a  temperature  of  from  100° 
to  105°  until  it  no  longer  lost  weight.  The  salt  then  contained  two 
molecules  of  water,  and  upon  strong  ignition  it  left  a  residue  of  MgO. 
The  percentage  of  MgO  in  the  oxalate  comes  out  as  follows  : 


7.2634  grm. 

oxalate  gave  1.9872  grm.  oxide. 

27.359  per  cent. 

6-3795 

1.7464 

27-375        " 

6.3653 

1.7418 

27-364       " 

6.2216 

1.7027 

27.368        " 

Mean, 

27.3665,  zb  .OO2 

3 

*  Journ.  fur  Prakt.  Chem.,  56,  310.     1852. 
f  Journ.  fi'ir  Prakt.  Chem.,  45,  473.     1848. 


138  THE    ATOMIC    WEIGHTS. 

In  three  of  these  experiments  the  MgO  was  treated  with  H2S04,  and 
converted,  as  by  Jacquelain  and  by  Bahr  in  their  later  researches,  into 
MgS04.  One  hundred  parts  of  MgO  gave  of  MgSO4  as  follows  : 

1.9872  grin.  MgO  gave  5.8995  grm.  MgSO4.  296.875 

1.7464  "  5-x783  "  296.513 

1.7418  "  5.1666  "  296.624 


Mean,  296. 67 r,  ±  .072 

In  1850  the  elaborate  investigations  of  Marchand  and  Scheerer  *  ap- 
peared. These  chemists  undertook  to  determine  the  composition  of 
some  natural  magnesites,  and,  by  applying  corrections  for  impurities,  to 
deduce  from  their  results  the  sought-for  atomic  weight.  The  magnesite 
chosen  for  the  investigation  was,  first,  a  yellow,  transparent  variety  from 
Snarum  ;  second,  a  white  opaque  mineral  from  the  same  locality  ;  and,, 
third,  a  very  pure  quality  from  Frankenstein.  In  each  case  the  im- 
purities were  carefully  determined  ;  but  only  a  part  of  the  details  need 
be  cited  here.  Silica  was  of  course  easily  corrected  for  by  simple  sub- 
traction from  the  sum  of  all  of  the  constituents;  but  iron  and  calcium,, 
when  found,  having  been  present  in  the  mineral  as  carbonates,  required 
the  assignment  to  them  of  a  portion  of  the  carbonic  acid.  In  the  atomic 
weight  determinations  the  mineral  was  first  dried  at  300°.  The  loss  in 
weight  upon  ignition  was  then  carbon  dioxide.  It  was  found,  however, 
that  even  here  a  correction  was  necessary.  Magnesite,  upon  drying  at 
300°,  loses  a  trace  of  C02,  and  still  retains  a  little  water ;  on  the  other 
hand,  a  minute  quantity  of  C02  remains  even  after  ignition.  The  C02 
expelled  at  300°  amounted  in  one  experiment  to  .054  per  cent. ;  that 
retained  after  calcination  to  .055  per  cent.  Both  errors  tend  in  the  same 
direction,  and  increase  the  apparent  percentage  of  MgO  in  the  magnesite. 
On  the  yellow  mineral  from  Snarum  the  crude  results  are  as  follows, 
giving  percentages  of  MgO,  FeO,  and  CO2  after  eliminating  silica : 

CO.,.  MgO.  FeO. 

51.8958  47-3278  .7764 

51.8798  47-3393  -7809 

51.8734  47.3154  -8112 

5'-*875  47.3372  .7753 

Mean,  47.3299,  ±  .0037 

After  applying  corrections  for  loss  and  retention  of  C02,  as  previously 
indicated,  the  mean  results  of  the  foregoing  series  become — 

CO.,.  MoO.  FeO. 

51.9931  47.2743  -7860 

The  ratio  between  the  MgO  and  the  C02,  after  correcting  for  the  iron, 
will  be  considered  further  on. 

*  Journ.  fi'ir  Prakt.  Chem.,  50,  385. 


MAGNESIUM.  139 

Of  the  white  magnesite  from  Snarum  but  a  single  analysis  was  made, 
which  for  present  purposes  may  be  ignored.  Concerning  the  Franken- 
stein mineral  three  series  of  analyses  were  executed.  In  the  first  series 
the  following  results  were  obtained  : 

8.996  grm.  CO2  =  8.2245  grm.  MgO.  47.760  per  cent.  MgO. 

7-960  "  7.2775         "  47.76i 

9-3265  8.529  47.767 

7-553  "  6.9095         "  47-775 


Mean,  47.766,  ±  .0022 

This  mean,  corrected  for  loss  of  C02  in  drying,  becomes  47.681.  I  give 
series  second  with  corrections  applied : 

6.8195  Srm-  MgCO3  gave  3.2500  grm.  MgO.          47.658  per  cent. 

11.3061  "  -               5-3849  "  47.628  " 

9-7375  "                4-635  ((  47-599  " 

12.3887  5.9033  «  47.650  « 

32.4148  15.453  47-674  " 

38.8912  18.5366  "  47.663  " 

26.5223  12.6445  "  47.675  " 

Mean,  47.650,  d=  .0069 

The  third  series  was  made  upon  very  pure  material,  so  that  the  cor- 
rections, although  applied,  were  less  influential.  The  results  were  as 
follows : 

4.2913  grm.  MgCO3  gave    2.0436  grm.  MgO.  47.622  per  cent. 

27.8286  "  13-2539         "  47.627       " 

14.6192  "  6.9692         "  47.672       " 

18.3085  '<  8.7237         "  47-648       " 

Mean,  47.642,  =fc  .0077 

In  a  supplementary  paper*  by  Scheerer,  it  was  shown  that  an  impor- 
tant correction  to  the  foregoing  data  had  Been  overlooked.  Scheerer,  re- 
examining  the  magnesites  in  question,  discovered  in  them  traces  of  lime, 
which  had  escaped  notice  in  the  original  analyses.  With  this  correction 
the  two  magnesites  in  question  exhibit  the  following  mean  composition  : 

Snarum.  Frankenstein. 

C02 52.131  52.338 

MgO 46.663  47-437 

CaO 430  . 225 

FeO. 776 


100.000  100.000 


Correcting  for  lime  and  iron,  by  assigning  each  its  share  of  C02,  the 
Snarum  magnesite  gives  as  the  true  percentage  of  magnesia  in  pure 


*  Ann.  d.  Chem.  und  Pharm.,  no,  240. 


140  THE    ATOMIC    WEIGHTS. 

magnesium  carbonate,  the  figure  47.624.  To  this,  without  serious  mis- 
take, we  may  assign  the  weight  indicated  by  the  probable  error,  ±  .0037, 
the  quantity  previously  deduced  from  the  percentages  of  MgO  given  in 
the  unconnected  analyses. 

From  the  Frankenstein  mineral,  similarly  corrected,  the  final  mean 
percentage  of  MgO  in  MgC03  becomes  47.628.  This,  however,  represents 
three  series  of  analyses,  whose  combined  probable  errors  may  be  prop- 
erly assigned  to  it.  The  combination  is  as  follows : 

dr  .OO22 
dz .0069 

±2  .0077 

Result,  ±  .0020,  probable  error  of  the  general  mean. 

We  may  now  combine  the  results  obtained  from  both  magnesites: 

Snarum  mineral Per  cent.  MgO,  47.624,  ±  .0037 

Frankenstein  mineral "  47.628,  d=  .0020 

General  mean Per  cent.  MgO,  47.627,  ±  .0018 

The  next  investigation  upon  the  atomic  weight  of  magnesium  which 
we  have  to  consider  is  that  of  Dumas.  *  Pure  magnesium  chloride  was 
placed  in  a  boat  of  platinum,  and  ignited  in  a  stream  of  dry  hydrochloric 
acid  gas.  The  excess  of  the  latter  having  been  expelled  by  a  current  of 
dry  carbon  dioxide,  the  platinum  boat,  still  warm,  was  placed  in  a  closed 
vessel  and  weighed  therein.  After  weighing,  the  chloride  was  dissolved 
and  titrated  in  the  usual  manner  with  a  solution  containing  a  known 
quantity  of  pure  silver.  The  weighings  which  Dumas  reports  give,  as 
proportional  to  100  parts  of  silver,  the  quantities  of  MgCL2  stated  in  the 
third  column : 

2.203  8rm-  MgCl2  =  4.964  grm.  Ag.  44.380 

2.5215  "  5.678  "  44.408 

2.363  5-325  "  44-376 

3.994  "  9.012  "  44.319 

2.578  5.834  "  44.189 

2.872  "  6.502  "  44.i7t 

2.080  4Jio  "  44.161 

2.214  "  5-°°2  "  44.262 

2.086  "  4.722  "  44.176 

1.688  <(  3823  "  44.154 

1.342  "  3.031  "  44.276 

Mean,  44.261,  dz  .020 

This  determination  gives  a  very  high  value  to  the  atomic  weight  of 
magnesium,  which  is  unquestionably  wrong.  The  error,  probably,  is 
due  to  the  presence  of  oxychloride  in  the  magnesium  chloride  taken,  an 

*Ann.  Chem.  Pharm.,  113,  33.     1860. 


MAGNESIUM. 


141 


impurity  tending  to  raise  the  apparent  atomic  weight  of  the  metal. 
Richards1  and  Parker's  revision  of  this  ratio  is  more  satisfactory. 

Marignac,  *  in  1883,  resorted  to  the  old  method  of  determination,  de- 
pending upon  the  direct  ratio  between  MgO  and  S03.  This  ratio  he 
measured  both  synthetically  and  analytically.  First,  magnesia  from 
various  sources  was  converted  into  sulphate.  The  MgS04  from  100  parts 
of  MgO  is  given  in  the  third  column : 

MgO.                  MgSO±.  Ratio. 

4.6620  298.17 

4.2025  298.32 

4.7480  298.30 

4.3855  298.23 

4.4060  298.15 

4-8530  298.33 

4.0740  298.37 

5.8390  298.29 

5.0600  298.26 

5.5715  298.26 

Mean,  298.27,  ±  .0149 

The  magnesia  for  experiments  1  to  5  was  prepared  by  calcination  of 
the  nitrate,  that  of  6  to  8  from  the  sulphate,  and  the  remaining  two  from 
the  carbonate.  But  Richards  and  Rogers  t  have  shown  that  magnesia 
derived  from  the  nitrate  always  contains  occluded  gaseous  impurity,  so 
that  the  experiments  depending  upon  its  use  are  somewhat  questionable. 
The  results  tend  to  give  an  atomic  weight  for  magnesium  which  is  pos- 
sibly too  high.  Whether  the  other  samples  of  magnesia  are  subject  to 
similar  objections  I  cannot  say. 

Marignac's  second  series  was  obtained  by  the  calcination  of  the  sul- 
phate, with  results  as  follows  : 


J 

.5635 

2    .      .... 

.4087 

3  

.5917 

4  

•  47O5 

c 

4778 

6 

6267 

7  

7657 

8 

.ocyt: 

Q 

606^ 

10.  . 

.8680 

MgSOv 

MgO. 

Ratio. 

3-7705                               i 

.2642 

298.25 

4.7396                              i 

.5884 

298.39 

3-3830 

.1345 

298.19 

4.7154 

.5806 

298.33 

4.5662 

.5302 

298.43 

4.5640 

.5300 

298.30 

3-2733 

.0979 

298.14 

4.8856 

.6378 

298.30 

5.0092 

.6792 

298.31 

5.3396 

.7898 

298.33 

5.1775 

.7352 

298.38 

5.0126 

.6807 

298.24 

5-0398 

.6894 

298.32 

Mean,  298  30,  ±  .0150 

*  Arch.  Sci.  Phys.  et  Nat.  (3),  10,  206. 
•f  Am.  Chem.  Journ.,  15,  567.     1893. 


142  THE    ATOMIC    WEIGHTS. 

These  data  may  now  be  combined  with  the  work  of  previous  investi- 
gators, giving  Macdonnell's  one  result  and  Jacquelain's  two,  each  equal 
weight  with  a  single  experiment  in  Bahr's  series: 

Macdonnell 300.193,  ±  .1413 

Jacquelain 297.968,  -b  .0999 

Bahr 296.200,  ±  .0815 

Svanberg  and  Nordenfeldt 296.671,  d=  .0720 

Marignac,  synthetic 298.27,     H~  .0149 

Marignac,  calcination 298.30,    dz  .0150 

General  mean 298. 210,  ±  .0103 

Burton  and  Vorce,*  who  published  their  work  on  magnesium  in  1890, 
started  out  with  the  metal  itself,  which  had  been  purified  by  distillation 
in  a  Sprengel  vacuum.  This  metal  was  dissolved  in  pure  nitric  acid, 
and  the  resulting  nitrate  was  converted  into  oxide  by  calcination  at  a 
white  heat.  The  oxide  was  carefully  tested  for  oxides  of  nitrogen,  which 
were  proved  to  be  absent,  but  occluded  gases,  the  impurity  pointed  out 
by  Richards  and  Rogers,  were  not  suspected.  This  impurity  must  have 
been  present,  and  it  would  tend  to  lower  the  apparent  atomic  weight  of 
magnesium  as  calculated  from  the  data  obtained.  The  results  were  as 
follows,  together  with  the  percentage  of  Mg  in  MgO : 

Mg  Taken.  MgO  Formed.  Per  cent.  Mg. 

.33009  .54766  60.273 

.34512  .57252  60.281 

.26058  .43221  60.290 

.28600  .47432  60.297 

.30917  .5^273  60.299 

.27636  .45853  60.271 

.36457  .60475  60.284 

.32411  .53746  60.304 

.32108  .53263  60.282 

.28323  .46988  60.262 


Mean,  60.2845,  =h  .0027 

The  latest  determinations  of  all  are  those  of  Richards  and  Parker,f 
who  studied  magnesium  chloride  with  all  the  precautions  suggested  by 
the  most  recent  researches.  The  salt  itself  was  not  only  free  from  oxy- 
chloride,  but  also  spectroscopically  pure  as  regards  alkaline  contamina- 
tions, and  all  weighings  were  reduced  to  a  vacuum  standard.  The  first 
series  of  experiments  gives  the  ratio  between  silver  chloride  and  mag- 
nesium chloride,  and  I  have  reduced  the  data  to  the  form  2AgCl :  MgCl2 :  : 
100  :  x.  The  weighings  and  values  for  x  are  subjoined  : 

*  Am.  Chem.  Journ.,  12,  219.     1890. 
fZeitsch.  Anorg.  Chem.,  13,  81.     1896. 


MAGNESIUM. 


143 


MgCl*. 

L  33550 
I.5I60I 


1.40664 
1.25487 


AgCl.  Ratio. 

4.01952  33-225 

4.56369  33-219 

3.98528  33.226 

4.23297  33-231 

3.77670  33  227 

Mean,  33.226,  ±  .0013 


The  remaining  series  of  experiments,  three  in  number,  relate  to  the  ratio 
2Ag  :  MgCl2,  which  was  earlier  investigated  by  Dumas.  For  the  elaborate 
details  of  manipulation  the  original  memoir  must  be  consulted.  I  can 
give  little  more  than  the  weights  found,  and  their  reduction  to  the  usual 
form  of  ratio,  Ag2 :  MgCl2 : :  100  :  x  : 


MgClv 

2.78284 
2.29360 
2-36579 


Second  Series. 

Ag.        ' 
6.30284 
5.19560 
5.35989 


Ratio. 
44.152 
44.145 
44.13° 

Mean,  44.142,  ±  .0043 


This  series  gives  slightly  higher  results   than  the  others,  and  the 
authors,  for  reasons  which  they  assign,  discard  it : 


Third  Series. 


MgCl*. 

1.99276 

1.78870 
2.12832 

2.51483 
2.40672 
1.95005 


4-05256 
4.82174 
5.69714 
545294 
4.41747 


Ratio. 

44.^31 
44.138 
44. 140 

44.I4I 


44-  H4 


Mean,  44.138,  =b  .0013 


The  fourth  series,  because  of  the  experience  gained  in  the  conduct  of 
the  preceding  determinations,  is  best  of  all,  and  the  authors  adopt  its 
results  in  preference  to  the  others : 

Fourth  Series. 

Ag.  Ratio. 

4.60855  44-136 

4.32841  44.138 

4.75635  44.137 

4.12447  44.137 

4o5I5I  44-138 

2.51876  44.138 

Mean,  44.137,  db  .0003 


2.03402 
1.91048 

2.09932 
1.82041 
1.92065 
1.11172 


144  THE    ATOMIC    WEIGHTS. 

These  series  combine  with  that  of  Dumas  as  follows : 

Dumas 44.261,  zb  .0200 

Richards  and  Parker,  second  series 44.142,  zb  .0043 

Richards  and  Parker,  third  series 44.138,  zb  .0013 

Richards  and  Parker,  fourth  series 44. 137,  db  .0x303 


General  mean 44. 138,  ±  .0003 

Here  the  first  two  values  practically  vanish,  and  the  third  and  fourth 
series  of  Richards  and  Parker  appear  alone. 

To  sum  up,  we  now  have  the  subjoined  ratios,  bearing  upon  the  atomic 
weight  of  magnesium  : 

(i.)   MgSO4  :  BaSO4  :  :  IOO  :  194.003,  ±  .021 

(2.)   MgO  :  MgSO4  :  :  100  :  298.210,  ±  .0103 

(3.)   Per  cent,  of  water  in  MgSO4,  7H3O,  51.21,  ±  .020 

(4.)   Per  cent,  of  MgO  in  oxalate,  27.3665,  ±  .0023 

(5.)   Per  cent,  of  MgO  in  carbonate,  47.627,  ±  .0018 

(6.)  Per  cent,  of  Mg  in  MgO,  60.2845,  ±  .0027 

(7.)  2Ag  :  Mgd2  :  :  IOO  :  44.138,  ±  .0003 

(8.)  2AgCl  :  MgCl2  :  :  100  :  33.226,  ±  .0013 

To  reduce  these  ratios  we  have — 

O  =  15.879,  zb  .0003  C    .  11.920,  zb  .0004 

Ag=:  107.108,  ±  .0031  Ba   =  136.392,  zb  .0086 

Cl  =  3S>179,  ±  -°°48  AgCl  =  142.287,  ±  .0037 
S  =  31.828,  zb  .0015 

For  the  molecular  weight  of  MgSO4,  two  values  are  now  calculable : 

From  (i) MgSO4=  119.450,  zb  .0137 

From  (3) "       =  119.239,^.0675 

General  mean MgSO4  ==  119.443,  ±  .0135 

Hence  Mg  =  24.099,  ±  .0136. 
For  MgO,  three  values  are  found  : 

From  (2) MgO  =  40.091,  zb  .0023 

From  (4) "     —  40.404,  dr  .0037 

From  (5) "     =:  39  721,  rb  .0021 

General  mean MgO  =  39.974,  =b  .0014 

Hence  Mg  =  24.095,  ±  .0014. 
For  MgCl2  there  are  two  values : 

From  (7) MgCl2  =  94-551,  db  -OO32 

From  (8) "       =94.553,^.0044 


General  mean MgCl2  =  94.552,  ±  .0026 

Hence  Mg  —  24.194,  ±  .0099. 


MAGNESIUM. 


145 


With  the  aid  of  these  intermediate  values,  four  estimates  of  the  atomic 
weight  of  magnesium  are  available,  as  follows  : 

From  molecular  weight  of  MgSO4.  ...    Mg  —  24.099,  ±  .0136 

•     From  molecular  weight  of  MgO "  =  24.095,  +  .0014 

From  molecular  weight  of  MgCl2 "  =  24. 194,  ±  .0099 

From  ratio  (6) "  —  24. 103,  db  .0020 


General  mean Mg  =  24.  TOO,  ±  .001 1 

If  0  =  16,  this  becomes  Mg  =  24.283. 

On  purely  chemical  grounds  the  third  of  the  foregoing  values,  that 
derived  from  magnesium  chloride,  seems  to  be  the  best.  I  should  un- 
hesitatingly adopt  it,  rejecting  the  others,  were  it  not  for  the  fact  that  it 
rests  upon  one  compound  of  magnesium  alone,  and  therefore  is  not  ab- 
solutely conclusive.  It  agrees  admirably,  however,  with  the  sulphate 
determinations  of  Marignac,  and  it  is  highly  probable  that  it  may  be 
fully  confirmed  later  by  evidence  from  other  sources. 

Marignac's  data,  taken  alone,  give  Mg  =  24.197.  The  fourth  series  of 
Richards  and  Parker,  by  itself,  gives  Mg  =  24.180.  The  approximate 
mean  of  these,  24.19,  may  be  preferred  by  many  chemists  to  the  general 
mean  derived  from  all  the  observations. 


10 


146  THE    ATOMIC   WEIGHTS. 


ZINC. 

The  several  determinations  of  the  atomic  weight  of  zinc  are  by  no 
means  closely  concordant.  The  results  obtained  by  Gay-Lussac*  and 
Berzelius  f  were  undoubtedly  too  low,  and  may  be  disregarded  here. 
We  need  consider  only  the  work  done  by  later  investigators. 

In  1842  Jacquelain  published  the  results  of  his  investigations  upon 
this  important  constant.  J  In  two  experiments  a  weighed  quantity  of 
zinc  was  converted  into  nitrate,  and  that  by  ignition  in  &  platinum  cruci- 
ble was  reduced  to  oxide.  In  two  other  experiments  sulphuric  acid 
took  the  place  of  nitric.  As  the  zinc  contained  small  quantities  of  lead 
and  iron,  these  were  estimated,  and  the  necessary  corrections  applied. 
From  the  weights  of  metal  and  oxide  given  by  Jacquelain  the  percent- 
ages have  been  calculated : 

Nitric  Series. 

9.917  grm.  Zn  gave  12.3138  grm.  ZnO.  80.536  per  cent.  Zn. 

9.809  "  12.1800         "  80.534  " 


Sulphuric  Series. 

2-398  grm.  Zn  gave  2.978  grm.  ZnO.  80.524 

3.197  "  3.968         "  80.570 


Mean  of  all  four,  80.541,  ±  .007 

Hence  Zn  =  65.723. 

The  method  adopted  by  Axel  Erdmann  §  is  essentially  the  same  as 
that  of  Jacquelain,  but  varies  from  the  latter  in  certain  important  details. 
First,  pure  zinc  oxide  was  prepared,  ignited  in  a  covered  crucible  with 
sugar,  and  then,  to  complete  the  reduction,  ignited  in  a  porcelain  tube 
in  a  current  of  hydrogen.  The  pure  zinc  thus  obtained  was  converted 
into  oxide  by  means  of  treatment  with  nitric  acid  and  subsequent  igni- 
tion in  a  porcelain  crucible.  Erdmann's  figures  give  us  the  following 
percentages  of  metal  in  the  oxide  : 

80.247 
80.257 
80.263 
80.274 


Mean,  80.260,  ±  .0037 

Hence  Zn  =  64.562. 


*  Memoire  d'Arceuil,  2,  174. 

tGilb.  Annal.,  37,  460. 

I  Compt.  Rend.,  14,  636. 

$  Poggend.  Annal.,  62,  611.     Berz.  lyehrb.,  3,  1219. 


ZINC.  147 

Upon  comparing  Erdmann's  results  with  those  of  Jacquelain  two 
points  are  worth  noticing  :  First,  Erdmann  worked  with  purer  material 
than  Jacquelain,  although  the  latter  applied  corrections  for  the  impuri- 
ties which  he  knew  were  present ;  secondly,  Erdmann  calcined  his  zinc 
nitrate  in  a  porcelain  crucible,  while  Jacquelain  used  platinum.  In  the 
latter  case  it  has  been  shown  that  portions  of  zinc  may  become  reduced 
and  alloy  themselves  with  the  platinum  of  the  crucible  ;  hence  a  lower 
weight  of  oxide  from  a  given  quantity  of  zinc,  a  higher  percentage  of 
metal,  and  an  increased  atomic  weight.  This  source  of  constant  error 
has  undoubtedly  affected  Jacquelain's  experiments,  and  vitiated  his 
results.  In  Erdmann's  work  no  such  errors  seem  to  be  present. 

Favre  *  employed  two  methods  of  investigation.  First,  zinc  was  dis- 
solved in  sulphuric  acid,  the  hydrogen  evolved  was  burned,  and  the 
weight  of  water  thus  formed  was  determined.  To  his  weighings  I  ap- 
pend the  ratio  between  metallic  zinc  and  100  parts  of  water : 

25.389  grm.  Zn  gave  6.928  grm.  H2O.  366.469 

30.369  "  8.297          "  366024 

31.776  "  8.671          "  366.463 

Mean,  366.319,  ±  .088 

Hence  Zn  =  65.494. 

The  second  method  adopted  by  Favre  was  to  burn  pure  zinc  oxalate, 
and  to  weigh  the  oxide  and  carbonic  acid  thus  produced.  From  the 
ratio  between  these  two  sets  of  weights  the  atomic  weight  of  zinc  is  easily 
deducible.  From  Favre 's  weighings,  if  C02  =  100,  ZnO  will  be  as  given 
in  the  third  column  below  : 

7.796  grm.  ZnO  =•  8.365  grm.  CO2.  93. 198 

7-342  "  7.883          "  93-137 

5.2065  "  5.588          "  93-173 

Mean,  93.169,  ±  .012 

Hence  Zn  =  65,521. 

Both  of  these  determinations  are  open  to  objections.  In  the  water 
series  it  was  essential  that  the  hydrogen  should  first  be  thoroughly  dried 
before  combustion,  and  then  that  every  trace  of  water  formed  should  be 
collected.  A  trivial  loss  of  hydrogen  or  of  water  would  tend  to  increase 
the  apparent  atomic  weight  of  zinc. 

In  the  combustion  of  the  zinc  oxalate  equally  great  difficulties  are 
encountered.  Here  a  variety  of  errors  are  possible,  such  as  are  due,  for 
example,  to  impurity  of  material,  to  imperfect  drying  of  the  carbon 
dioxide,  and  to  incomplete  collection  of  the  latter.  Indeed  a  fourth 
combustion  is  omitted  from  the  series  as  given,  having  been  rejected  by 
Favre  himself.  In  this  case  the  oxide  formed  was  contaminated  by  traces 
of  sulphide. 

'Ann.  Chim.  Phys.  (3),  10,  163.     1844. 


148  THE    ATOMIC    WEIGHTS. 

Baubigny,*  in  1883,  resorted  to  the  well-known  sulphate  method. 
Zinc  sulphate,  elaborately  purified,  was  dried  at  440°  to  constant  weight, 
and  then  calcined  at  a  temperature  equal  to  the  fusing  point  of  gold. 
These  data  were  obtained: 

ZnSO4.  ZnO.  Per  cent.  ZnO. 

6.699  3.377  50-4io 

8.776  4.4245  50-416 


Mean,  50.413,  ±  .0020 

Hence  Zn  =  64.909. 

In  Marignac's  determinations  of  the  atomic  weight  of  zinc,  published 
also  in  1883,f  there  is  a  peculiar  complication.  After  testing  and  criti- 
cising some  other  methods,  he  finally  decided  to  study  the  double  salt 
K2ZnCl4,  which,  however,  is  difficult  to  obtai  n  in  absolutely  definite  con- 
dition. Although  the  compound  was  purified  by  repeated  crystalliza- 
tions, it  was  found  to  deliquesce  readily,  and  thereby  to  undergo  partial 
dissociation,  losing  chloride  of  zinc,  and  leaving  the  porous  layer  on  the 
crystalline  surfaces  richer  in  potassium.  In  order  to  evade  this  diffi- 
culty, Marignac  placed  a  large  quantity  of  the  salt  in  a  funnel,  and  col- 
lected the  liquid  product  of  deliquescence  as  it  ran  down.  In  this 
product  he  determined  chlorine  by  volumetric  titration  with  a  standard 
solution  of  silver,  and  also  estimated  zinc  by  precipitation  with  sodium 
carbonate,  and  weighing  as  oxide.  From  the  data  thus  obtained  equa- 
tions were  formed,  giving  for  each  a  nalysis  an  atomic  weight  of  zinc 
which  is  independent  of  the  proportion  between  ZnCl2  and  KC1  in  the 
substance  analyzed.  The  data  unfortunately  are  too  bulky  for  repro- 
duction here  and  the  calculations  are  complex ;  but  the  results  found  for 
zinc,  when  Ag  =  107.93,  Cl  —  35.457,  and  K  =  39.137,  are  as  follows  : 

1.  One  titration Zn  —  65.22 

2.  Two  titrations 65.37 

3.  Two  titrations  ...    65.31 

4.  Two  titrations 65.28 

5.  One  titration 65. 26 

Each  of  these  values  represents  a  distinct  sample  of  the  deliquesced 
material,  and  the  number  of  chlorine  determinations  is  indicated. 

A  second  set  of  determinations  was  made  by  the  same  analytical 
method  directly  upon  the  recrystallized  and  carefully  dried  K2ZnCl4. 
The  values  for  Zn  are  as  follows  : 

6.  Two  titrations N. Zn  =  65.28 

7.  Two  titrations 65.39 

8.  One  titration 65.32 

*  Ccmpt.  Rend.,  97,  906.     1883. 
tArch.  Sci.  Phys.  et  Nat.  (3),  10,  194. 


ZINC.  149 

In  order  to  adapt  these  data  to  the  uniform  scheme  of  calculation  em- 
ployed in  this  work,  taking  into  account  their  probable  error  and  the 
probable  errors  of  the  antecedent  values  for  K,  Cl,  and  Ag,  it  seems  to 
be  best  to  calculate  them  back  with  the  atomic  weights  used  by  Marignac 
into  the  form  of  the  ratio  A£4  :  K2  Z  nd4  :  :  100  :  x.  Doing  this,  and  tak- 
ing each  value  as  many  times  as  there  are  titrations  represented  in  it  — 
that  is,  giving  the  results  of  a  double  determination  twice  the  weight  of  a 
single  one  —  we  have  the  following  series  of  data  for  the  ratio  in  question  : 

From  1  ...................................      66.090 

From  2.. 


66.124 

f  66.  no 
From  3  ....................................  { 

l66.no 

f  66.104 
P  rom  4  ....................................  < 

166.104 

From  5  ....................................     66.099 

f  66.104 
P  rom  6  ....................................  4 

(.  66.104 

f  66.129 
From  7   ...................................  \ 

166.129 

From  8  ...................................     66.113 


Mean,  66.111,  d=  .0023 

Hence,  from  Marignac's  work,  Ag4  :  K2ZnCl4  : :  100 :  66.111,  ±  .0023,  a 
ratio  which  can  be  discussed  along  with  others  at  the  close  of  this  chapter. 

During  the  years  between  1883  and  1889,  a  number  of  determinations 
were  made  of  the  direct  ratio  between  zinc  and  hydrogen — that  is, 
weighed  quantities  of  zinc  were  dissolved  in  acid,  the  hydrogen  evolved 
was  measured,  and  from  its  volume,  with  Regnault's  data,  the  weight  of 
H  was  computed.  First  in  order  are  Van  der  Plaats'  determi nations j* 
whose  results,  as  given  by  himself,  are  subjoined.  The  weights  are 
reduced  to  a  vacuum.  Sulphuric  acid  was  the  solvent. 

Zn,  grms.  H,  litres.  Zn  = 

6.6725  1.1424  65.21 

9.1271  i.5643  65.14 

13.8758  2.3767  65.18 

Mean,  65.177,  ±  .0137 

With  the  new  value  for  the  weight  of  hydrogen,  .089872  gramme  per 
litre,  this  becomes  Zn  =  64.980,  db  .0137. 

Reynolds  and  Ramsay  made  29  determinations  of  this  ratio.f  rejecting, 
however,  all  but  5.  The  weighings  were  reduced  to  vacuum,  and  in  each 
experiment  the  volume  of  hydrogen  was  fixed  by  the  mean  of  seven  or 
eight  readings.  The  values  for  Zn  are  as  follows : 

*  Compt.  Rend.,  100,  52.     1885. 
f  Journ.  Chem.  Soc.,  51,  854.     1887. 


150  THE    ATOMIC    WEIGHTS. 

65.5060 
65.4766 

65.4450 
65.5522 
65.4141 


Mean,  65.4787,  rh  .0161 

These  values  were  computed  with  Regnault's  data  for  the  weight  of  H. 
Corrected  by  the  new  value  the  mean  becomes  Zn  =  65.280,  ±  .0161. 

A  few  determinations  by  Mallet  were  made  incidentally  to  his  work  on 
the  atomic  weight  of  gold,  and  appear  in  the  same  paper.*  According 
to  these  experiments,  one  gramme  of  zinc  gives — 

341.8500.  H.,  and  Zn  =  65.158 
341.91       "  "          65.146 

341-93       "  65.143 

342.04      "  "          65.122 


Mean,  65.142,  ±  .0039 

In  this  case  the  Crafts-Regnault  weight  of  H  was  taken,  one  litre  — 
.08979  gramme.     Corrected,  the  mean  gives  Zn  =  65.082,  ±  .0039. 

Two  other  series  of  determinations  of  questionable  value  remain  to 
be  noticed  before  leaving  the  consideration  of  the  direct  H  :  Zn  ratio. 
They  represent  really  the  practice  work  of  students,  and  are  interesting 
as  an  illustration  of  the  closeness  with  which  such  work  can  be  done. 
The  first  series  was  made  in  the  laboratory  of  the  Johns  Hopkins  Uni- 
versity, under  the  direction  of  Morse  and  Keiser,f  and  contains  51  deter- 
minations, as  follows  : 


64.68 

65.74 

65.40 

65.26 

64.72 

64.80 

65.32 

65.26 

65.20 

65.20 

64.74 

64.40 

65.60 

64.72 

65.00 

64.60 

65.10 

64.40 

65.00 

64.76 

65-24 

65.68 

64.90 

64.60 

65.38 

64.92 

64.80 

65.06 

64.64 

65.H 

64.84 

65.24 

64.84 

64.88 

64.72 

64.82 

65.00 

65.20 

64.80 

65.08 

65.12 

64.40 

65.06 

66.40 

64.60 

64.74 

64.60 

64.80 

65.12 

65.60 

64.74 

Mean  of  all,  Zn  =  64.997,  ±  .0328 

*Amer.  Chern.  Journ.,  12,  205.     1890. 
f  Amer.  Chem.  Journ.,  6,  347.     1884. 


ZINC.  151 

Corrected  for  the  difference  between  Regnault's  value  for  H  and  the 
new  value,  this  becomes  Zn  =  64.800,  ±  .0328. 

The  second  student  series  was  published  by  Torrey,*  who  gives  15 
determinations,  as  follows : 


65.36  64.96 

65.30  64.70 

64.92  65.00 

64.72  64.78 

65.04  64.44 

64.80  65.24 

65.20  64.92 
64.90 
Mean,  64.952,  dr  .0436 

Corrected  as  in  the  other  series,  this  gives  Zn  —  64.755,  ±  .0436. 
The  five  corrected  means  for  the  ratio  H  :  Zn  may  now  be  combined, 
thus : 

Van  der  Plaats 64.980,  ±  .0137 

Reynolds  and  Ramsay 65.280,  ±  .0161 

Mallet 65.082,  ±  .0039 

Morse  and  Keiser 64.800,  ±  .0328 

Torrey 64.755,  ±  .0436 


General  mean 65.079,  ±  .0036 

Morse  and  Burton,  f  in  their  determinations  of  the  atomic  weight  of 
zinc,  returned  essentially  to  the  old  method  adopted  by  Erdmann  and 
by  Jacquelain.  Their  zinc  was  obtained  spectroscopically  pure  by  dis- 
tillation in  a  vacuum,  and  was  oxidized  by  nitric  acid  which  left  abso- 
lutely no  residue  upon  evaporation.  The  conversion  to  oxide  was 
effected  in  a  porcelain  crucible,  which  was  enclosed  in  a  larger  one,  and 
the  ignition  of  the  nitrate  was  carried  out  in  a  muffle.  In  weighing,  the 
crucible  was  tared  by  one  of  nearly  equal  weight.  Results  as  follows : 

Wf.  Zn.  Wt.  ZnO.  Percent.  Zn  in  ZnO. 


.11616 

1.38972 

80.320 

.03423 

1.28782 

80.308 

.11628 

1.38987 

80.315 

.05760 

1.31681 

80.316 

.04801 

1.30492 

80.313 

.02957 

1.28193 

80.318 

.09181 

1.35944 

80.315 

[.16413 

1-44955 

80.305 

.07814 

1.34248 

80.305 

.12754 

1.40400 

80.306 

.91112 

1.13446 

80.310 

*  Amer.  Chem.  Journ.,  10,  74,     1888. 
t  Anier.  Chem.  Journ.,  10,  311.     1888. 


152  THE    ATOMIC    WEIGHTS. 

i.iooii  1.36981 

1.17038  1^45726 

1.03148  1.28436 

L05505  I.3I365 

Mean,  80.3115,  ±00084. 

Combining  this  mean  with  the  means  found  by  the  earlier  investigators, 
we  have — 

Jacquelain 80.541,    ±  .0070 

Erdmann 80.260,     ±  .0037 

Morse  and  Burton 80.3115,  d=  .00084 

General  mean 80.317,    ±  .0008 

Morse  and  Burton  verified  by  experiment  the  stability  of  oxide  of  zinc 
at  the  temperatures  of  ignition,  and  found  that  it  did  not  dissociate. 
They  also  proved  the  absence  of  oxides  of  nitrogen  from  the  zinc  oxide. 
The  investigations  of  Richards  and  Rogers,*  however,  have  shown  that 
zinc  oxide  prepared  by  ignition  of  the  nitrate  always  carries  gaseous 
occlusions,  so  that  the  atomic  weight  of  zinc  computed  from  the  data  of 
Morse  and  Burton  is  probably  too  low.  But  for  that  objection,  their  work 
would  leave  little  to  be  desired  on  the  score  of  accuracy. 

The  determinations  made  by  Gladstone  and  Hibbard  f  represent  still 
another  process  for  measuring  the  atomic  weight  of  zinc.  Zinc  was  dis- 
solved in  a  voltameter,  and  the  same  current  was  used  to  precipitate 
metallic  silver  or  copper  in  equivalent  amount.  The  weight  of  zinc  dis- 
solved, compared  with  the  weight  of  the  other  metal  thrown  down,  gives 
the  atomic  weight  sought  for.  Two  voltameters  were  used  in  the  experi- 
ments, giving  duplicate  estimates  for  zinc  with  reference  to  each  weigh- 
ing of  silver  or  copper.  The  silver  series  is  as  follows,  with  the  ratio 
Ag2 :  Zn  :  :  100  :  x  in  the  third  column  : 


Zn. 

4r- 

Ratio. 

.7767 

2.5589 

30.353 

.7758 

2.5589 

30.318 

.5927 

1.9551 

30.316 

.5924 

1.9551 

30.300 

.2277 

•7517 

30.291 

.2281 

.7517 

30.345 

•  7452 

2.4588 

30.307 

•7475 

2.4588 

30.401 

.  .8770 

2.9000 

30.241 

.8784 

2.9000 

30.290 

•  9341 

3.0809 

30-3!9 

.9347 

3.0809 

30.339 

Mean,  30.318,  =b  .0077 

*  Proc.  Amer.  Acad.,  1893,  200. 

t  Journ.  Chem.  Soc.,  55,  443.     1889. 


ZINC. 


153 


To  the  copper  series  I  add  the  ratio  Cu  :  Zn  :  :  100  :  x. 


Zn. 

.7767 
.7758 
.5927 
.5924 
.2277 
.2281 
.8770 
.8784 
•9341 
•9347 


Cu. 

.7526 
.7526 
•  5737 
•5737 
.2209 
.2209 
.8510 
.8510 
.9038 
.9038 


Ratio. 

103-13 
103.08 

I03-31 
103.26 
103.08 
103.26 
103.05 
103.22 
103.36 
103.42 

Mean,  103.22,  =fc  .0261 


Richards  and  Rogers,*  in  their  investigation  of  the  atomic  weight  of 
zinc,  studied  the  anhydrous  bromide.  This  was  prepared  by  solution 
of  zinc  oxide  in  hydrobromic  acid,  evaporation  to  dryness,  and  subse- 
quent distillation  in  an  atmosphere  of  carbon  dioxide.  In  some  experi- 
ments, however,  the  bromide  was  heated  in  an  atmosphere  of  nitrogen, 
mingled  with  gaseous  hydrobromic  acid.  All  water  can  thus  be  removed, 
without  formation  of  oxy bromides. 

The  zinc  bromide  so  obtained  was  dissolved  in  water,  and  precipitated 
with  a  solution  containing  a  known  amount  of  silver  in  the  form  of 
nitrate.  The  silver  bromide  was  weighed  on  a  Gooch  crucible,  and  the 
ratio  2AgBr:  ZnBr2  thus  found.  An  excess  of  silver  was  always  used, 
and  in  one  series  of  experiments  it  was  estimated  by  precipitation  with 
hydrobromic  acid.  Deducting  the  excess  thus  found  from  the  original 
quantity  of  silver,  the  amount  of  the  latter  proportional  to  the  zinc 
bromide  was  found;  hence  the  ratio  Ag2 :  ZnBr2.  The  results,  with 
vacuum  weights,  are  as  follows : 

Series  A. 

ZnBr.2.  AgBr.  Ratio. 

1.69616  2.82805  59.976 

1.98198  3.3045o  59-978 

1.70920  2  84949  59-984 

2.35079  3-9'94i  59.978 

2.66078  4-4375 l  59.96i 

Mean,  59.975,  ±  .0034 


Series  B. 

ZnBr^. 

Ag. 

AgBr. 

Ag  Ratio. 

AgBr  Ratio. 

2.33882 

2.  24063 

3.90067 

104.382 

59-959 

1.97142 

1.88837 

3.28742 

104.398 

59.969 

2.14985 

2.05971 

3-58539 

104.376 

59.96i 

2.00966 

1.92476 

3-35074 

104  411 

59-977 

Mean,  104.392, 

Mean,  59.967, 

±  .0054 

=b  .0027 

*Zeitsch.  Aiiorg.  Chem.,  10,  i.     1895. 


154  THE   ATOMIC   WEIGHTS. 

At  the  end  of  the  same  paper,  Richards  alone  gives  two  more  series  of 
determinations  made  upon  zinc  bromide  prepared  by  the  action  of  pure 
bromine  upon  pure  electrolytic  zinc.  The  bromide  so  obtained  was 
further  refined  by  sublimation  or  distillation,  and  dried  by  heating  in  a 
stream  of  carbon  dioxide  and  gaseous  hydrobromic  acid.  Thus  was 
ensured  the  absence  of  basic  salts  and  of  water.  The  weights  and  results 
found  in  the  two  series  were  as  follows : 

Series  C. 

ZnBrv  .                         Ag.  Ratio. 

6.23833  5-9766  104.379 

5  26449  5-0436  104.380 

9.36283  8.9702  104.377 

Mean,  104.379,  ±  .0007 

Series  D. 

ZnBr.2.  AgBr.  Ratio. 

2.65847  4.43358  59.962 

2.30939  3-85149  59.96i 

5.26449  8.77992  59-961 


Mean,  59.961,  ±  .0004 

In  some  details  of  manipulation  these  series  differ  from  those  given 
by  Richards  and  Rogers  jointly,  but  their  minutiaB  are  not  essential  to 
the  present  discussion. 

Combining  these  several  series,  we  have — 

For  Ag^  :  ZnBr^  :  :  100  :  x. 

Series  E 104.392,  ±  .0054 

Series  C 104.379,  ±  .0007 

General  mean 104.380,  ±  .0007 

For  2  AgBr  :  ZnBr^  :  :  zoo  :  x. 

Series  A 59-975,  ±  .0034 

Series  B 59.967,  =b  .0027 

Series  D.. 59. 961,  d=  .0004 

General  mean 59.962,  ±  .0004 

From  the  Ag  ratio ZnBr2  =  223.599,  ±  .0066 

From  the  AgBr  ratio "      —  223.601,  ±  .0066 


General  mean ZnBr2  —  223.600,  ±  .0047 

And  Zn  =    64.912,  d=  .0133 


ZINC.  155 

For  computing  the  atomic  weight  of  zinc  we  now  have  these  ratios: 

(i.)  Per  cent.  Zn  in  ZnO,  80.317,  ±  .0008 

(2.)  Per  cent.  ZnO  in  ZnSO4,  50.413,  rb  .0020 

(3.)  H2O  :  Zn  :  :  100  :  366.319,  ±  .088 

(4.)  2CO2  :  Zn  :  :  100  :  93.169,  rb  -OI2 

(5.)  H  :  Zn  :  :  I  :  65.079,  ±  .0036 

(6.)  Ag4  :  K2ZnCl4  :  :  100  :  66. in,  ±  .0023 

(7.)  Ag2  :  Zn  :  :  100  :  30.318,  ±  .0077 

(8.)  Cu  :  Zn  :  :  100  :  103.22,  =b  .0261 

(9.)  Ag2  :  ZnBr2  :  :  100  :  104.38,  rb  .0007 

(10.)  2AgBr  :  ZnBr2  :  :  100  :  59.962,  rb  .0004 

The  antecedent  atomic  weights,  with  H  =  1,  are — 

O     —     15.879,  rb  .0003  C          =     11.920,  rb  .0004 

Cl   =    35.179,  ±  .0048  S          =    31.828,  rb  .0015 

Br  =    79.344,  rb  .0062  Cu       —    63.119,  rb  .0015 

Ag  =  107.108,  rb  .0031  AgBr  =  186.452,  rb  .0054 
K    =    38.817,  rb  .0051 

With  these  data,  combining  ratios  9  and  10  into  one  (see  preceding 
paragraphs),  we  have  nine  independent  values  for  the  atomic  weight  of 
zinc,  as  follows : 

From  (i) Zn  =  64.795,  d=  .0030 

From  (2) "  =  64.909,  rb  .0073 

From  (3) "  =  65.494,  rb  .0019 

From  (4) "  =65.521,  rb  .0115 

From  (5) "  =  65.079,  rb  .0036 

From  (6) "  =  64.891,  rb  .0253 

From  (7) "  =  64.947,  rb  .0166 

From  (8) "  =65.151,  ±  .0166 

From  (9)  and  (10) "  =  64.912,  rb  .0133 


General  mean  of  all Zn  =  65.152,  ±  .0014 

With  O  =  16 Zn  =  65.650 

Of  these  values,  Nos.  3  and  4,  representing  Favre's  work,  are  unques- 
tionably far  wrong.  Rejecting  them,  the  general  mean  of  the  remaining 
seven  values  becomes — 

Zn  =  64.912,  ±  .OO2I. 

If  0  =  16,  this  gives  Zn  =  65.407.  These  figures  are  identical,  except 
as  regards  the  lower  probable  error,  with  the  result  deduced  from  Rich- 
ards and  Rogers'  determinations  alone,  and  they  may  be  taken  as 
satisfactory. 


156  THE   ATOMIC    WEIGHTS. 


CADMIUM. 

The  earliest  determination-  of  the  atomic  weight  of  this  metal  was  by 
Stromeyer,  who  found  that  100  parts  of  cadmium  united  with  14.352  of 
oxygen.*  With  our  value  for  the  atomic  weight  of  oxygen,  these  figures 
make  Cd  =  110.64.  This  result  has  now  only  a  historical  interest. 

The  more  modern  estimates  of  the  atomic  weight  of  cadmium  begin 
with  the  work  of  v.  Hauer.f  He  heated  pure  anhydrous  cadmium  sul- 
phate in  a  stream  of  dry  hydrogen  sulphide,  and  weighed  the  cadmium 
sulphide  thus  obtained.  His  results  were  as  follows,  with  the  percent- 
age of  CdS  in  CdS04  therefrom  deduced  : 

7.7650  grm.  CdSO4  gave  5.3741  grm.  CdS.  69.209  per  cent. 

6.6086  "  4.5746  "  69.222  " 

7-3821  "  $.1117  "  69.245  " 

6.8377  "  4.7336  "  69.228  « 

8.1956  "  5.6736  "  69.227  " 

7.6039  "  5.2634  "  69.220  " 

7.1415  4-9431  69.217  " 

5.8245  4.0335  69.251  " 

6.8462  4.74I5  69.257  " 

Mean,  69.231,  ±  .0042 

LenssenJ  worked  upon  pure  cadmium  oxalate,  handling,  however, 
only  small  quantities  of  material.  This  salt,  upon  ignition,  leaves  the 
following  percentages  of  oxide : 

.5128  grm.  oxalate  gave  .3281  grm.  CdO.  63.982  per  cent. 

.6552  "  .4193          "  63.996       " 

.4017  .2573  64.053      " 

Mean,  64.010,  d=  .014 

Dumas  1 1  dissolved  pure  cadmium  in  hydrochloric  acid,  evaporated 
the  solution  to  dryness,  and  fused  the  residue  in  hydrochloric  acid  gas. 
The  cadmium  chloride  thus  obtained  was  dissolved  in  water  and  titrated 
with  a  solution  of  silver  after  the  usual  manner.  From  Dumas'  weigh- 
ings I  calculate  the  ratio  between  CdCl2  and  100  parts  of  silver : 

2-369  grm.  CdCl2  =  2.791  grm.  Ag.  84.880 

4.540  "  5.348         "  84.892 

6.177  "  7-260         "  85.083 

2.404  "  2.841          "  84.618 

3.5325  "  4.166         "  84.794 

4.042  "  4.767         «  84.791 

Mean,  84.843,  ±  .026 

*  See  Berz.  Lehrbuch.  sth  Aufl.,  3,  1219. 
t  Journ.  fiir  Prakt.  Chem.,  72,  350.     1857. 
t  Journ.  fi'ir  Prakt.  Chem.,  79,  281.     1860. 
||  Ann.  Chem.  Pharm.,  113,  27.     1860. 


CADMIUM.  157 

Next  in  order  comes  Huntington's*  work,  carried  out  in  the  laboratory 
of  J.  P.  Cooke.  Bromide  of  cadmium  was  prepared  by  dissolving  the 
carbonate  in  hydrobromic  acid,  and  the  product,  dried  at  200°,  was  puri- 
fied by  sublimation  in  a  porcelain  tube.  Upon  the  compound  thus  ob- 
tained two  series  of  experiments  were  made. 

In  one  series  the  bromide  was  dissolved  in  water,  and  a  quantity  of 
silver  not  quite  sufficient  for  complete  precipitation  of  the  bromine  was 
then  added  in  nitric  acid  solution.  After  the  precipitate  had  settled, 
the  supernatant  liquid  was  titrated  with  a  standard  solution  of  silver 
containing  one  gramme  to  the  litre.  The  precipitate  was  washed  by  de- 
cantation,  collected  by  reverse  filtration,  and  weighed.  To  the  weigh- 
ings I  append  the  ratio  between  CdBr2  and  100  parts  of  silver  bromide  : 

1.5592  grm.  CdBr2  gave  2.1529  grm.  AgBr.  Ratio,  72.423 

*  3.7456  5-I724  "  "  72.4i5 
2.4267  3.3511  "  "  72.415 

*  3.6645  5.0590  «  "  72.435 

*  3.7679  5.2016  "  "  72.437 
2.7938  3-8583  "  "  72.4io 

*  i. 9225  2.6552  "  "  72.405 
3-4473               "  4-7593  "  "  72.433 


Mean,  72.4216,  ±  .0028 

The  second  series  was  like  the  first,  except  that  the  weight  of  silver 
needed  to  effect  precipitation  was  noted,  instead  of  the  weight  of  silver 
bromide  formed.  In  the  experiments  marked  with  an  asterisk,  both  the 
amount  of  silver  required  and  the  amount  of  silver  bromide  thrown  down 
were  determined  in  one  set  of  weighings.  The  third  column  gives  the 
CdBr2  proportional  to  100  parts  of  silver: 

*  3. 7456  grm.  CdBr.2=:  2.9715  grm.  Ag.  126.051 
5.0270  "  3.9874  "  126.072 

*  3.6645  "  2.9073  "  126.045 

*  3.7679  "  2.9888  "  126.067 

*  1. 9225  "  1.5248  "  126.082 
2.9101  "  2.3079  "  126.093 
3.6510  "  2.8951  "  126.110 
3.9782  "  3.1551  "  126.088 

Mean,  126.076,  ±  .0052 

According  to  Huntington's  own  calculations,  these  experiments  fix  the 
ratio  between  silver,  bromine,  and  cadmium  as  Ag  :  Br  :  Cd  : :  108  :  80  • 
112.31. 

In  1890,  Partridge f  published  determinations  of  the  atomic  weight 
of  cadmium,  made  by  three  methods,  the  weighings  being  reduced  to 

*  Proc.  Araer.  Acad.,  1881. 

t  Amer.  Journ.  Sci.  (3),  40,  377.     1890. 


158 


THE   ATOMIC    WEIGHTS. 


vacuum  standards  throughout.     First,  Leiissen's  method  was  followed, 
viz.,  the  ignition  of  the  oxalate,  with  the  subjoined  results: 


CdC.,0,. 
.09898 
.21548 
.10711 
.17948 
.16066 

•17995 
•34227 

.43154 
•53510 
.41311 


CdO. 
.70299 
.77746 
.70807 
•75440 
.74327 
•75471 
.85864 

.91573 
.98197 
.80397 


Percent.  CdO. 
63.966 
63.962 
63.957 
63.959 
63.959 
63.964 
63.968 
63-970 
63.968 
63-971 


Mean,  63.964,  ±  .0010 


Second!}7,  v.  Hauer's  experiments  were  repeated,  cadmium  sulphate 
being  reduced  to  sulphide  by  heating  in  a  stream  of  H2S.  The  following 
data  were  obtained  : 


1.60514 

1.55831 
1.67190 
1.66976 
1.40821 
1.56290 
1.63278 
1.58270 

1.53873 
1.70462 


as. 

Percent.  CdS. 

.11076 

69.204 

.07834 

69.197 

.15669 

69.185 

.15554 

69.200 

.9745° 

69.202 

.08156 

69.205 

.12985 

69.194 

.09524 

69.198 

.06481 

69.201 

.17962 

69.201 

Mean,  69.199,  =h  .0012 
v.  Hauer  found,  69.231,  ±  .0042 


General  mean,  69.202,  ±  .0012 

In  the  third  set  of  determinations  cadmium  oxalate  was  transformed 
to  sulphide  by  heating  in  H2S,  giving  the  ratio  CdC204 :  CdS  :  :  100 :  x. 


1.57092 

1.73654 
2.19276 

1.24337 
1.18743 
1.54038 

1-38905 
2.03562 
2.03781 
1.91840 


CdS. 
1.13065 
1.24979 
1.57825 

.89492 

.85463 
1.10858 

•99974 
1.46517 
1.46658 
1.38075 


Per  cent  CdS. 
71.972 
71.973 
71-974 
7L974 
71-975 
71.968 
71.976 
71.979 
71.970 
71.971 


Mean,  71.973,  =b  .0007 


CADMIUM.  159 

This  work  of  Partridge  was  presently  discussed  by  Clarke,*  with  ref- 
erence to  the  concordance  of  the  data,  and  it  was  shown  that  the  three 
ratios  determined  could  be  discussed  algebraically,  giving  values  for  the 
atomic  weights  of  Cd,  S,  and  C,  when  0  =  16.  These  values  are — 

Cd=  111.7850 
C  =  11.9958 
S  =  32.0002, 

and  are  independent  of  all  antecedent  values  except  that  assumed  for 
the  standard,  oxygen. 

Morse  and  Jones,  f  starting  out  from  cadmium  purified  by  fractional 
distillation  in  vacuo,  adopted  two  methods  for  their  determinations. 
First,  they  effected  the  synthesis  of  the  oxide  from  known  weights  of 
metal  by  dissolving  the  latter  in  nitric  acid,  evaporating  to  dryness,  and 
subsequent  ignition  of  the  product.  The  oxide  thus  obtained  was  found 
to  be  completely  free  from  oxides  of  nitrogen.  The  weighings,-which  are 
given  below,  were  made  in  tared  crucibles.  The  third  column  gives  the 
percentage  of  Cd  in  CdO. 

Cd  Taken,  CdO  Found.  Per  cent.  Cd. 

.77891  2.03288  87.507 

.82492  2.08544  87.508 

.74688  1.99626  87.507 

.57000  1.79418  87.505 

.481  2.26820  87.506 

.27297  2.59751  87.504 

.75695  2.00775  87.508 

.70028  1.94305  87.505 

.92237  2.19679  87.508 

.92081  2.19502  87.508 

Mean,  87.5066,  rb  .00032 

The  second  method  employed  by  Morse  and  Jones  was  that  of  Lenssen 
with  cadmium  oxalate.  This  salt  they  find  to  be  somewhat  hygroscopic, 
a  property  against  which  the  operator  must  be  on  his  guard.  The  data 
found  are  as  follows  : 

CdC2Ot.  CdO.  Percent.  CdO.' 

•53937  .98526  64.004 

.77483  1.13582  63996 

.70211  1.08949  64.008 

.70238  1.08967  64.004 

.74447  1.11651  64.003 

Mean,  64.003,  ±  .0042 

Lorimer  and  Smith,  like  Morse  and  Jones,  determined  the  atomic 
weight  of  cadmium  by  means  of  the  oxide,  but  by  analysis  instead  of 

*Am.  Chem.  Jourii.,  13,  34.     1891. 
t  Am.  Chem.  Journ.,  14,  261.     1892. 


160  THE   ATOMIC    WEIGHTS. 

synthesis.     Weighed  quantities  of  oxide  were  dissolved  in  potassium 

cyanide  solution,  from  which  metallic  cadmium  was  thrown  down  elec- 

trolytically.     The  weights  are  reduced  to  vacuum  standards. 

CdO  Taken.                    Cd  Found.  Per  cent.  Cd. 

.34767                              .30418  87.491 

.41538                              -36352  87.515 

1.04698                              .91618  87.507 

1.04066                               .915°°  87.493 

1.26447                              1.10649  87.506 

.78493                               .68675  87.492 

.86707                               .75884  87.518 

.67175                               -58785  87.510 

1.44362                              1.26329  87.508 

Mean,  87.5044,  ±  .0023 

Mr.  Bucher's  dissertation*  upon  the  atomic  weight  of  cadmium  does 
not  claim  to  give  any  final  measurements,  but  rather  to  discuss  the  vari- 
ous methods  by  which  that  constant  has  been  determined.  Neverthe- 
less, it  gives  many  data  which  seem  to  have  positive  value,  and  which 
are  certainly  fit  for  discussion  along  with  those  which  have  preceded 
this  paragraph.  Bucher  begins  with  cadmium  purified  by  distillation 
nine  times  in  vacuo,  and  from  this  his  various  compounds  were  prepared. 
His  first  series  of  determinations  was  made  by  reducing  cadmium  oxalate 
to  oxide,  the  oxalate  having  been  dried  fifty  hours  at  150°.  The  reduc- 
tion was  effected  by  heating  in  jacketed  porcelain  crucibles,  with  various 
precautions,  and  the  results  obtained,  reduced  to  vacuum  standards,  are 
as  follows  : 

Oxalate.  Oxide.  Percent.  Oxide. 

.97674  1.26414  63.951 

.94912  1.24682  63.968. 

.96786  1.25886  63.971 

.87099  1.19675  .  63.958 

•3755°  -87994  63.972 

.33313  .85308  63.991 

94450  1.24452  64.002 

2.01846  1.29210  64.014 

Mean,  63.978,  d=  .0052 

Combining  this  with  the  means  found  by  previous  experimenters,  we 
have  for  the  percentage  of  oxide  in  oxalate — 

Lenssen 64.010,  ±  .0140 

Partridge 63.962,  ±.  .0010 

Morse  and  Jones. 64.003,  ±  .0042 

Bucher 63.978,  ±  .0052 

General  mean 63.966,  ±  .0010 

*  "An  examination  of  some  methods  employed  in  determining  the  atomic  weight  of  cadmium." 
Johns  Hopkins  University  doctoral  dissertation.     By  John  B.  Bucher.     Baltimore,  1895. 


CADMIUM. 


161 


Bucher's  next  series  of  determinations  was  by  Partridge's  method — 
the  conversion  of  cadmium  oxalate  into  cadmium  sulphide  by  heating 
in  a  stream  of  sulphuretted  hydrogen.  The  sulphide  was  finally  cooled 
in  a  current  of  dry  nitrogen.  The  vacuum  weights  and  ratios  are  sub- 
joined : 

Oxalate.  Sulphide.  Percentage. 

2.56319  1.84716  72.065 

2.18364  I-5734I  72.055 

2.11643  1.52462  72.037 

3.13105  2.25582  72.047 

Mean,  72.051,  =b  .0127 
Partridge  found,  71.973,  ±  .0007 

General  mean,  71.974,  ±  .0007 

Here  Bucher's  mean  practically  vanishes. 

The  third  method  employed  by  Bucher  was  that  of  weighing  cadmium 
chloride,  dissolving  in  water,  precipitating  with  silver  nitrate,  and  weigh- 
ing the  silver  chloride  found.  The  cadmium  chloride  was  prepared, 
partly  by  solution  of  cadmium  in  hydrochloric  acid,  evaporation  to 
dryness,  and  sublimation  in  vacuo;  and  partly  by  the  direct  union  of 
the  metal  with  chlorine.  The  silver  chloride  was  weighed  in  a  Gooch 
crucible,  with  platinum  sponge  in  place  of  the  asbestos.  To  the  vacuum 
weights  I  append  the  ratio  2AgCl  :  CdCl2  :  :  100  :  x. 


3.09183 
2.26100 

1-35729 

2.05582 

1.89774 

3-5°367 

2.70292 

4.24276 

3.40200 

4.60659 

2.40832 

2.19144 

2.84628 

2.56748 

2.31003 

.25008 

.96015 

.29787 

.94227 

.10976 

.63080 


AgCl. 

4.83856 

3.53854 
2.12431 
3.21727 
2.97041 

5.48473 
4.23087 
6.63598 

5-323r4 
7.20386 


3.42724 

4-45477 
4.01651 
3.61370 
1.95652 
3-°654i 
3-59391 
3.03811 

1.73547 
2.55016 


Ratio. 
63.900 
63.896 

63-893 
63.899 
63.886 
63.880 
63.886 
63.936 
63.910 
63.946 
63.930 
63.942 

63-893 
63923 
63.924 
63-893 
63.944 
63.938 

63.9'5 
63.946 

63-949 


Mean,  63.916,  ±  .0032 

Bucher  gives  a  rather  full  discussion  of  the  presumable  errors  in  this 
method,  which,  however,  he  regards  as  somewhat  compensatory. 
11 


The 


162  THE   ATOMIC    WEIGHTS. 

series  is  followed  by  a  similar  one  with  cadmium  bromide,  the  latter 

having  been  sublimed  in  vacuo.     Results  as  follows : 

CdBr2.  AgBr.  Ratio. 

4.39941  6.07204  72.454 

3.18030  4-38831  72.472 

3.60336  4.97I50  72.480 

4.04240  5-58062  72.453 

3.60505  4.97519  72.461 

Mean,  72.464,    ±  .0035 
Huntington  found,  72.4216,  ±  .0028 


General  mean,  72.438,    ±  .0022 

In  order  to  fix  a  minimum  value  for  the  atomic  weight  of  cadmium, 
Bucher  effected  the  synthesis  of  the  sulphate  from  the  metal.  1.15781 
grammes  of  cadmium  gave  2.14776  of  sulphate. 

Hence  Cd  =.-  111.511.       , 

The  sulphate  produced  was  dried  at  400°,  and  afterwards  examined 
for  free  sulphuric  acid,  giving  a  correction  which  was  applied  to  the 
weighings.  The  corrected  weight  is  given  above.  Any  impurity  in  the 
sulphate  would  tend  to  lower  the  apparent  atomic  weight  of  cadmium, 
and  therefore  the  result  is  believed  by  the  author  to  be  a  minimum. 

Finally,  Bucher  examined  the  oxide  method  followed  by  Morse  and 
Jones.  The  syntheses  of  oxide  were  effected  in  double  crucibles,  first 
with  both  crucibles  porcelain,  and  afterwards  with  the  small  inner  cruci- 
ble of  platinum.  Two  experiments  were  made  by  the  first  method,  three 
by  the  last.  Weights  and  percentages  (Cd  in  CdO)  as  follows : 

Cd.  CdO.  Percentage. 

{1.26142  1.44144  87.511 

.99785  1.14035  87.504 

Mean,  87.508 

^1.11321  1.27247  87.484 

4  1.02412  1.17054  87.491 

(2.80966  3.21152  87.487 


Mean,  87.487 
Mean  of  alias  one  series,  87.495,  ±  .0035 

The  two  means  given  above,  representing  work  done  with  porcelain 
and  with  platinum  crucibles,  correspond  to  a  difference  of  about  0.2  in 
the  atomic  weight  of  cadmium.  Experiments  were  made  with  pure 
oxide  of  cadmium  by  converting  it  into  nitrate  and  then  back  to  oxide, 
exactly  as  in  the  foregoing  syntheses.  In  each  case  the  oxide  obtained 
at  the  end  of  the  operation  represented  an  increase  in  weight,  but  the 
increase  was  greater  in  platinum  than  in  porcelain.  Hence  the  weigh- 
ings of  cadmium  oxide  in  the  foregoing  determinations  probably  are 
subject  to  constant  errors,  and  cannot  be  trusted  to  fix  the  atomic  weight 


CADMIUM. 


163 


of  cadmium.  Their  mean,  taken  in  one  series,  has  really  no  significance ; 
but  as  the  computations  in  this  work  involve  a  study  of  compensation 
of  errors,  the  data  may  be  combined  with  their  predecessors,  as  follows : 

Morse  and  Jones 87.5066,  ±  .00032 

Lorimer  and  Smith 87.5044,  rh  .0023 

Bucher 87.495,    ±  .0035 

General  mean 87.5064,  db  .0003 

This  is  equivalent  to  the  absolute  rejection  of  Buchers  data,  and  is 
therefore  not  wholly  fair  to  them.  His  work  throws  doubt  upon  the 
validity  of  the  ratio,  as  determined,  altogether. 

The  latest  determinations  relative  to  the  atomic  weight  of  cadmium 
are  those  of  Hardin.,*  who  effected  the  electrolysis  of  the  chloride  and 
bromide,  and  also  made  a  direct  comparison  between  cadmium  and 
silver.  The  aqueous  solutions  of  the  salts,  mixed  with  potassium 
cyanide,  were  electrolyzed  in  platinum  dishes.  The  cadmium  which 
served  as  the  starting  point  for  the  investigation  was  purified  by  distil- 
lation in  hydrogen.  All  weights  are  reduced  to  a  vacuum.  The  data 
for  the  chloride  series  are  as  follows,  with  a  column  added  for  the  per- 
centage of  Cd  in  CdCla : 


Weight  CdClv 

.43  HO 

.49165 

.71752 

.72188 

.77264 

.81224 

.90022 
1.02072 
1.26322 
L52344 


Weight  Cd. 

.26422 
.30112 
•43942 
.44208 


.49742 

.55135 
.62505 

.77365 
•933*4 


Percentage  Cd. 
61.247 
61.247 
61.241 
61.241 
61.245 
61.240 
61.246 
61.236 
61.244 
61.252 

Mean,  61.244,  ±  .0010. 


The  results  for  the  bromide,  similarly  stated,  are  these: 


Weight  CdBr^. 

Weight  Cd. 

Percentage  Cd. 

.57745 

.23790 

41.198 

.76412 

.31484 

41.203 

.91835 

.37842 

41.207 

.01460 

.41808 

41.206 

•I5°74 

.474H 

41.203 

•24751 

•51392 

41.196 

•25951 

.51905 

41.210 

•51805 

.62556 

41.208 

•63543 

.67378 

4i.i99 

2.15342 

.88722 

4  1  .  200 

Mean,  41.203,  ±0010. 

'  Journ.  Amer.  Gheni.  Soc.,  18,  1016.     1896. 


164  THE   ATOMIC   WEIGHTS. 

The  direct  comparison  of  cadmium  and  silver  was  effected  by  the 
simultaneous  electrolysis,  in  the  same  current,  of  double  cyanide  solu- 
tions. Silver  was  thrown  down  in  one  platinum  dish,  and  cadmium  in 
another.  The  process  was  not  altogether  satisfactory,  and  gave  diver- 
gent results,  those  which  are  cited  below  having  been  selected  by  Har- 
din  from  the  mass  of  data  obtained.  I  have  added  in  a  third  column 
the  cadmium  proportional  to  100  parts  of  silver  : 

Weight  Cd.  Weight  Ag.  Ratio. 

.12624  -24335  5L876 

.11032  .21262  51.886 

.12720  .24515  51.887 

.12616  -24331  51-852 

.22058  .42520  51-877 


Mean,  51.876,  d=  .0041 

For  cadmium  we  now  have  the  following  ratios : 

(I.)  Per  cent,  of  Cd  in  CdO,  87.5064,  ±  .0003 
(2.)  Per  cent,  of  CdO  in  CdC2O4,  63.966,  ±  .0010 
(3.)  Per  cent,  of  CdS  from  CdC2O4,  71.974,  ±  .0007 
(4.)   Per  cent,  of  CdS  from  CdSO4,  69.202,  dz  .0012 
(5.)  Ag2  :  CdCl2  :  :  100  :  84.843,  ±  .0260 
(6.)  2AgCl  :  CdCl2  :  :  100  :  63.916,  ±  .0032 
(7.)   Ag2  :  CdBr2  :  :  100  :  126.076,  ±  .0052 
(8.)  2AgBr  :  CdBr2  :  :  100  :  72.438,  ±  .0022 
(9.)  Per  cent,  of  Cd  in  CdG2,  61.244,  ±  .0010 

(10.)  Per  cent  of  Cd  in  CdBr2,  41.203,  =b  .0010 

(il.)  2Ag  :  Cd  :  :  100  :  51.876,  ±  .0041 

Bucher's  single  experiment  upon  the  synthesis  of  the  sulphate,  although 
important  and  interesting,  cannot  carry  weight  enough  to  warrant  its 
consideration  in  connection  with  the  other  ratios,  and  is  therefore  not 
included. 

The  antecedent  values,  for  use  in  computation  are — 

O  ±=  I5-879,  ±  .0003  S    =  31.828,  =b  .0015 

Ag  =  107.108,  d=  .0031  C    =  11.920,  dr  .0004 

Cl  ==  35.179,  ±  .0048  AgCl  =  142.287,  ±  ,0037 

Br  =  79.344,  ±  .0062  AgBr  =  186.452,  ±  .0054 

For  the  molecular  weight  of  cadmium  chloride,  two  values  are  now 
deducible : 

From  (5) CdCl2  =  181.739,  ±  .0560 

From  (6) "      —  181.888,  +  .0103 

General  mean CdCl2  =  181.883,  ±  .0138 

Hence  Cd  =  111.525,  ±  .0138. 


CADMIUM.  165 

For  cadmium  bromide  we  have — 

From  (7) CdBr2  =  270.073,  =b  .0136 

From  (8) "      =  270.124,^.0113 


General  mean CdBr2  =  270.105,  ±  .0087 

Hence  Cd  =  111.417,  ±  .0151. 

For  cadmium  there  are  nine  independent  values,  as  follows  : 

From  (3) Cd  =  1 10.793,  d=  .0081 

From  (4) "  =  i 10.890,  ±  .0069 

From  (2) "  =  1 1 1.004,  db  -OO47 

From  (11) "  =  111.127,  ±  -0095 

From  (9) "  =  1 1 1. 183,  ±  .0155 

From  (10) "  =  111.202,  ±  .0093 

From  (i). "  =  111.227,  ±  -0034 

From  molecular  weight  CdBr2 "  =  111.417,  =b  .0151 

From  molecular  weight  CdCl2  .......  ".=  111.525,  ±  .0138 

General  mean Cd  =  iii.ioo,  dz  .0022 

If  0=16,  Cd=  111.947. 

This  result  is  obviously  uncertain.  The  data  are  far  from  being  con- 
clusive, however,  and  I  am  therefore  inclined  to  trust  the  mean  rather 
than  any  one  of  the  values  taken  separately.  It  is  quite  possible  that 
the  highest  of  all  the  figures  may  be  nearest  the  truth,  as  Bucher's  ex- 
periments seem  to  indicate ;  but  until  new  evidence  is  obtained  it  would 
hardly  be  wise  to  make  any  selection.  The  mean  obtained  agrees  well 
with  the  data  of  Morse  and  Jones,  Lorimer  and  Smith,  and  Hardin. 


166  THE    ATOMIC    WEIGHTS. 


MERCURY. 

In  dealing  with  the  atomic  weight  of  mercury  we  may  reject  the  early 
determinations  by  Sefstrom*  and  a  large  part  of  the  work  done  by  Tur- 
ner, f  The  latter  chemist,  in  addition  to  the  data  which  will  be  cited 
below,  gives  figures  to  represent  the  percentage  composition  of  both  the 
chlorides  of  mercury ;  but  these  results  are  neither  reliable  nor  in  proper 
shape  to  be  used. 

First  in  order  we  may  consider  the  percentage  composition  of  mercuric 
oxide,  as  established  by  Turner  and  by  Erdmann  and  Marchand.  In 
both  investigations  the  oxide  was  decomposed  by  heat,  and  the  mercury 
was  accurately  weighed.  Gold  leaf  served  to  collect  the  last  traces  of 
mercurial  vapor. 

Turner  gives  four  estimations.  Two  represent  oxide  obtained  by  the 
ignition  of  the  nitrate,  and  two  are  from  commercial  oxide.  In  the  first 
two  the  oxide  still  contained  traces  of  nitrate,  but  hardly  in  weighable 
proportions.  A  comparison  of  the  figures  from  this  source  with  the  others 
is  sufficiently  conclusive  on  this  point.  The  third  column  represents  the 
percentage  of  mercury  in  HgO  : 

144  805  grains  Hg  =  11.54  grains  O.  92.619  per  cent. 

125.980  "  10.08       "  92.592       " 

I73-561  "  13.82       "  92.625       " 

114.294  "  9.101       "  92.620       " 


Mean,  92.614,  db  .0050 

In  the  experiments  of  Erdmann  and  Marchand  J  every  precaution  was 
taken  to  ensure  accuracy.  Their  weighings,  reduced  to  a  vacuum  stand- 
ard, give  the  subjoined  percentages  : 

82.0079  grm.  HgO  gave  75.9347  grm.  Hg.  92.594  per  cent. 

51.0320  47.2538       "  92.597       " 

84.4996  "  78.2501        "  92.604       " 

44-6283  "  41-3285       "  92.606       " 

118.4066  "  109.6408       "  92.597        " 


Mean,  92.5996,  ±  .0015 

Hardin's  determination  of  the  same  ratio,  being  different  in  character, 
will  be  considered  later. 

With  a  view  to  establishing  the  atomic  weight  of  sulphur,  Erdmann 
and  Marchand  also  made  a  series  of  analyses  of  pure  mercuric  sulphide. 
These  data  are  now  best  available  for  discussion  under  mercury.  The 

*Sefstrom.    Berz.  L,ehrb.,  5th  ed.,  3,  1215.     Work  done  in  1812. 

fPhil.  Trans.,  1833,  531-535. 

J  Journ.  fur  Prakt.  Chem.,  31,  395.     1844. 


MERCURY.  167 

v 

sulphide  was  mixed  with  pure  copper  and  ignited,  mercury  distilling 
over  and  copper  sulphide  remaining  behind.  Gold  leaf  was  used  to 
retain  traces  of  mercurial  vapor,  and  the  weighings  were  reduced  to 
vacuum  : 

34.3568  grm.  HgS  gave  29.6207    grm.  Hg.  86.215  Per  cent-  Hg. 

24.8278  "  21.40295         "  86.206  " 

37.2177  "  32.08416         "  86.207  " 

80.7641  "  69.6372  "  86.223  " 

Mean,  86.2127,  ±  .0027 

For  the  percentage  of  mercury  in  mercuric  chloride  we  have  data  by 
Turner,  Millon,  Svanberg,  and  Hardin.  Turner,*  in  addition  to  some 
precipitations  of  mercuric  chloride  by  silver  nitrate,  gives  two  experi- 
ments in  which  the  compound  was  decomposed  by  pure  stannous 
chloride,  and  the  mercury  thus  set  free  was  collected  and  weighed.  The 
results  were  as  follows  : 

44.782  grains  Hg  =  15.90  grains  CI.  73-798  per  cent. 

73.09  "  25.97         "  73.784       " 

Mean,  73.791,  ±  .005 

Millon  f  purified  mercuric  chloride  by  solution  in  ether  and  sublima- 
tion, and  then  subjected  it  to  distillation  with  lime.  The  mercury  was 
collected  as  in  Erdmann  and  Marchand's  experiments.  Percentages  of 
metal  as  follows  : 

73-87 
73-8i 
73-83 
73-87 


Mean,  73.845,  ±  .010 

Svanberg,  J  following  the  general  method  of  Erdmann  and  Marchand, 
made  three  distillations  of  mercuric  chloride  with  lime,  and  got  the 
following  results : 

12.048  grm.  HgC)2  gave  8.889    grm.  Hg.  73.780  per  cent. 

12.529  "  9-24S6         "  73-794       " 

12.6491  "  9-3363         "  73-8io       " 

Mean,  73.795,  ±  .006 

The  most  recent  determinations  of  the  atomic  weight  of  mercury  are 
due  to  Hardin,§  whose  methods  were  entirely  electrolytic.  First,  pure 
mercuric  oxide  was  dissolved  in  dilute,  aqueous  potassium  cyanide,  and 

*Phil.  Trans.,  1833,  53I-535- 
fAnn.  Chirn.  Phys.  (3),  18,  345.     1846. 
I  Journ.  fur  Prakt.  Chem.,  45,  472.     1848. 
I  Journ.  Amer.  Chem.  Soc.,  18,  1003.    '1896. 


168  THE   ATOMIC    WEIGHTS. 

electrolyzed  in  a  platinum  dish.  Six  determinations  are  published,  out 
of  a  larger  number,  but  without  reduction  of  the  weights  to  a  vacuum. 
The  data,  with  a  percentage  column  added,  are  as  follows : 

Weight  HgO.  Weight  Hg.                    Per  cent.  Hg. 

.26223  .24281  92.594 

.23830  .22065  92.593 

.23200  .21482  92.595 

.14148  .13100  92.593 

.29799  .27592  92.594 

.19631  .18177  92.593 

Mean,  92.594,  d=  0003. 

Various  sources  of  error  were  detected  in  these  experiments,  and  the 
series  is  therefore  rejected  by  Hardin.  It  combines  with  previous  series 
as  follows : 

Turner % 92.614,    rfc  .0050 

Erdmann  and  Marchand 92.5996,  ±  .0015 

Hardin 92. 594,     ±  .0003 


General  mean 92-595,    rb  .0003 

Hardin  also  studied  mercuric  chloride,  bromide,  and  cyanide,  and  the 
direct  ratio  between  mercury  and  silver,  with  reduction  of  weights  to  a 
vacuum.  Electrolysis  was  conducted  in  a  platinum  dish,  as  usual. 
With  the  chloride  and  bromide,  the  solutions  were  mixed  with  dilute 
potassium  cyanide.  The  data  for  the  chloride  are  as  follows,  the  per- 
centage column  being  added  by  myself: 

Weight  HgCLv  Weight  Hg.  Per  cent.  Hg. 

•45932  -33912 

•54735  -40415 

.56002  .41348 

.63586  .46941 

.64365  .47521 

.73281  .54101 

.86467  .63840 

1.06776  .78825 

1.07945  .79685  . 

1.51402  1.11780  73-830 

Mean,  73.829,  ±  .0012 


Combining  this  with  the  earlier  determinations,  we  hav 


Turner 73-791,  db  .0050 

Millon 73.845,  ±  .0100 

Svanberg 73-795,  ±  .0060 

Hardin 73.829,  ±  .001 2 

General  mean 73.826,  d=  .001 1 


MERCURY. 


169 


For  the  bromide  Hardin's  data  are  — 


Weight  HgBrv 
.70002 


•57*42 

.77285 

.80930 

.85342 

1.11076 

i  17270 

1.26186 

1.40142 


And  for  the  cyanide  — 

Weight  HgC2  N2. 

.55776 

.63290 

.70652 

.80241 

.65706 

.81678 
1.07628 
1.22615 
1.66225 
2.11170 


Weight  Hg. 
.38892 
.3135° 
.3i750 
.42932 
.44955 
.47416 
.61708 
.65145 
.70107 
.77870 


Weight  Hg. 

.44252 
.50215 

.56053 
.63663 
.52130 
.64805 
.85392 
.97282 

1.31880 

1.67541 


Per  cent.  Hg. 

55-558 
55-555 
55-563 
55-550 
55.548 
55-56o 
55-555 
55-551 
55-559 
55-565 


Mean,  55.556,  ±  .0012 


Per  cent.  Hg. 

79-337 
79-341 
79-337 
79-340 
79-338 
79-342 
79-340 
79-339 
79-338 
79-339 

Mean,  79.339,  ±  .0004 


In  the  last  series  cited  no  potassium  cyanide  was  used,  but  the  solution 
of  mercuric  cyanide,  with  the  addition  of  one  drop  of  sulphuric  acid, 
was  electrolyzed  directly. 

The  direct  ratio  between  silver  and  mercury  was  determined  by  throw- 
ing down  the  two  metals,  simultaneously,  in  the  same  electric  current. 
Both  metals  were  taken  in  double  cyanide  solution.  With  Hardin's 
equivalent  weights  I  give  a  third  column,  showing  the  quantity  of  mer- 
cury corresponding  to  100  parts  of  silver.  Many  experiments  were  re- 
jected, and  only  the  following  seven  are  published  by  the  author : 


Weight  Hg. 

.06126 
.06190 
.07814 
.10361 
.15201 
.26806 
.82808 


Weight  Ag. 
.06610 
.06680 
.08432 
.11181 
.  1 6402 
.28940 
.89388 


Ratio. 
92.678 
92.665 
92.671 
92.666 
92.678 
92.626 
92.639 


Mean,  92.660,  ±  .0051 


170  THE   ATOMIC    WEIGHTS. 

We  now  have  six  ratios  involving  the  atomic  weight  of  mercury,  as 
follows  : 

(i.)  Per  cent,  of  Hg  in  HgO,  92.595,  ±  .0003 

(2.)  Per  cent,  of  Hg  in  HgS,  86.2127,  =b  .0027 

(3.)  Per  cent,  of  Hg  in  HgCla>  73.826,  ±  .0011 

(4.)  Per  cent,  of  Hg  in  HgBr2,  55.556,  ±  .0012 

(5.)  Per  cent,  of  Hg  in  HgC2N2,  79.339,  ±  .0004 

(6.)  2Ag  :  Hg  :  :  100  :  92.660,  ±  .0051 

The  calculations  involve  the  following  values  : 

O  =  15.879,  ±-.0003  Br=r  79.344,  ±  .0062 

Ag=  107.108,  ±.0031  S  =31.828,  ±.0015 

Cl  =  35.179,  ±  .0048  C  =  11.920,  ±  .0004 

N  =  13.935,  ±  .0021 

Hence  the  values  for  mercury  are — 

From  (I) Hg  =  198.557,  ±  .0084 

From  (2) "    =  199.027,  H=  .0406 

From  (3) "    =  198.482,  ±  .0285 

From  (4) "    =  198.364,^.0170 

From  (5) «    —  198.568,  ±  .0170 

From  (6) "    =  198.493,  ±  .0124 

General  mean Hg  =  198.532,  db  .0059 

If  0=  16,  Hg  =  200.045. 

But  according  to  Hardin  the  value  derived  from  the  analyses  of  mer- 
curic oxide  is  untrustworthy.  Rejecting  this,  and  also  the  abnormally 
high -result  from  the  sulphide  series,  the  general  mean  of  the  four  re- 
maining values  is — 

Hg  =  198.491,  ±  .0083, 

or,  with  0  =  16,  Hg  =  200.004.     These  figures  seem  to  be  the  best  for 
the  atomic  weight  of  mercury. 


BORON.  171 


BORON. 

In  the  former  edition  of  this  work  the  data  relative  to  boron  were  few 
and  unimportant.  There  was  a  little  work  on  record  by  Berzelius  and 
by  Laurent,  and  this  was  eked  out  by  a  discussion  of  Deville's  analyses 
of  boron  chloride  and  bromide.  As  the  latter  were  not  intended  for 
atomic  weight  determinations  they  will  be  omitted  from  the  present  re- 
calculation, which  includes  the  later  researches  of  Hoskyns-Abrahall, 
Ramsay  and  Aston,  and  Rimbach. 

Berzelius*  based  his  determination  upon  three  concordant  estima- 
tions of  the  percentage  of  water  in  borax.  Laurent  f  made  use  of  two 
similar  estimations,  and  all  five  may  be  properly  put  in  one  series,  thus  : 

47-10] 

47.10  j-  Berzelius. 
47-ioj 

47-  '5  I  Laurent. 

47-20* 

Mean,  47.13,  ±  .013 

In  1892  the  posthumous  notes  of  the  late  Hoskyns-Abrahall  were 
edited  and  published  by  Ewan  and  Hartog.  J  This  chemist  especially 
studied  the  ratio  between  boron  bromide  and  silver,  and  also  redeter- 
mined  the  percentage  of  water  in  crystallized  borax.  The  latter  work, 
which  was  purely  preliminary,  although  carried  out  with  great  care,  gave 
the  following  results,  reduced  to  vacuum  standards  : 


Na^BtPv  Per  cent. 

7.00667                           3.69587  47.2069 

12.95936                           6.82560  47.3308 

4.65812                           2.45248  47.3504 

4.47208                             3-93956  47.2763 

4.94504                             2.60759  47.2686 

Mean,  47.2866,  db  .0171 

Two  sets  of  determinations  were  made  with  the  bromide,  which  was 
prepared  from  boron  and  bromine  directly,  freed  from  excess  of  the 
latter  by  standing  over  mercury,  and  finally  collected,  after  distillation, 
in  small,  weighed,  glass  bulbs.  It  was  titrated  with  a  solution  of  silver 
after  all  the  usual  precautions.  The  first  series  of  experiments  was  as 
follows,  with  BBr3  proportional  to  100  parts  of  silver  stated  as  the  ratio  : 

*Poggend.  Annalen,  8,  i.     1826. 

t  Journ.  fur  Prakt.  Chem.,  47,  415.     1849. 

I  Journ.  Chem.  Soc.,  61,  650.     August,  1892. 


-v  • 


v,  .-  - 


' 


v,  :v 

-  :.-S,v 

-  :x-     ; 
-.  .    :;-^ 


•\". 


--   ---  = 


--  •--.-  = 


.   . 


:  :  — 


.  .  : 

--• 
- 

•-' 
-    '  : 


:  : 

----- 


::  ;- 


L>- 


174  THE   ATOMIC   WEIGHTS. 

Na^B^O,.  AgCl.  Ratio. 

5.3118  7.5259  70.580 

4.7806  6.7794  70.517 

4.9907  7.0801  70.489 

4.7231  6.6960  70.536 

3.3138  4-6931  70.610 

Mean,  70.546,  ±  .0146 

Rimbach  *  based  his  determination  of  the  atomic  weight  of  boron  upon 
the  fact  that  boric  acid  is  neutral  to  methyl  orange,  and  that  therefore 
it  is  possible  to  titrate  a  solution  of  borax  directly  with  hydrochloric 
acid.  His  borax  was  prepared  from  carefully  purified  boric  acid  and 
sodium  carbonate,  and  his  hydrochloric  acid  was  standardized  by  a  series 
of  precipitations  and  weighings  as  silver  chloride.  It  contained  1.84983 
per  cent,  of  actual  HC1.  The  borax,  dissolved  in  water,  was  titrated  by 
means  of  a  weight-burette.  I  give  the  weights  found  in  the  first  and 
second  columns  of  the  following  table,  and  in  the  third  column,  calcu- 
lated by  myself,  the  HC1  proportional  to  100  parts  of  crystallized  borax. 
Rimbach  himself  computes  the  percentage  of  Na2O  and  thence  the  atomic 
weight  of  boron,  but  the  ratio  Na2B407.10H20  :  2HC1  is  the  ratio  actually 
determined. 

Na^B^O-f.wH^O.  HCl  Solution.  Ratio. 

10.00214  103.1951  19.0853 

15.32772  158-1503  19.0864 

15.08870  155-7271  19.0917 

10.12930  104.5448  19.0922 

5.25732  54-2571  19.0908 

15.04324  155-2307  19.0883 

15-04761  I55-2959  19.0908 

10.43409  107.6602  19.0868 

5.04713  52.0897  i9-°9I5 

Mean,  19.0893,  d=  .0006     , 

Obviously,  this  error  should  be  increased  by  the  probable  errors  in- 
volved in  standardizing  the  acid,  but  they  are  too  small  to  be  worth 
considering. 

The  following  ratios  are  now  available  for  boron  : 

(1)  Percentage  of  water  in  Na2B4O7.ioH2O,  47.1756,  =h  .0066 

(2)  3Ag  :  BBr3  :  :  100  :  77.425,  ±  .0017 

(3)  Na2B4O7  :  2NaCl  :  :  100  :  57-933,  ±  .0074 

(4)  2AgCl  :  Na2B4O7  :  :  100  :  70.546,  +  .0146 

(5)  Na2B4O7.ioH2O  :  2HC1  :  :  100  :  19.0893,  ±  .0006 

*  Berichte  Deutsch.  Chein.  Gesell.,  26,  164.     1893. 


BORON.  175 

For  reduction  we  have  the  antecedent  atomic  and  molecular  weights — 

O    =    15-879,  ±  -0003  Na      =    22.881,  ±  .0046 

Ag=  107.108,  ±  .0031  NaCl=;    58.060,  ±  .0017 

Cl  =    35.179,^.0048  AgCl=  142.287,  rb  .0037 
Br  =    79-344,  =b  .0062 

For  the  molecular  weight  of  Na2B407  we  now  have — 

From  (i) . . .  .' Na2B4O7  =  200. 198,  ±  .0377 

From  (3) "        =  200.439,  ±  .0263 

From  (4) "        =  200.756,  ±  .0419 

From  (5) "        =  200.260,  ±  .0518 

General  mean Na2B4Ot  =  200.421,  ±  .0180 

Hence  B  =  10.876,  ±  .0051. 

From  ratio  (2),  B  =  10.753,  ±  .0207.     The  two  values  combined  give— 

B  =1  10.863,  ±  .0050. 

Or,  if  0  =  16,  B  ==  10.946. 

If  we  consider  ratios  (1),  (3),  (4),  and  (5)  separately,  they  give  the  fol- 
lowing values  for  B : 

From  (i) B  =  10.821 

From  (3) "  =  10.881 

From  (4) "  =  10.960 

From  (5) "  =  10.836 

Of  these,  the  second  and  third  involve  the  data  from  which,  in  a 
previous  section  of  this  work,  the  ratio  NaCl :  AgCl  was  computed.  In 
using  that  ratio  for  measuring  the  molecular  weights  of  its  component 
molecules,  discordance  was  noted,  which  again  appears  here.  The  chief 
uncertainty  in  it  seems  to  be  connected  with  ratio  (4),  which  is  therefore 
entitled  to  comparatively  little  credence,  although  its  rejection  is  not 
necessary  at  this  point.  In  ratio  (2),  Abrahall's  determination,  the  high 
probable  error  of  B  is  due  to  the  also  high  probable  error  of  3Br,  and  it 
is  quite  likely  that  the  result  is  undervalued.  The  general  mean,  B  = 
10.863,  ±  .0050,  however,  can  hardly  be  much  out  of  the  way.  It  is  cer- 
tainly more  probable  than  any  one  of  the  individual  values. 


176  THE    ATOMIC    WEIGHTS. 


ALUMINUM. 

The  atomic  weight  of  aluminum  has  been  determined  by  Berzelius, 
Mather,  Tissier,  Dumas,  Isnard,  Terrell,  Mallet,  and  Baubigny.  The 
early  calculations  of  Davy  and  of  Thomson  we  may  properly  disregard. 

Berzelius'  *  determination  rests  upon  a  single  experiment.  He  ignited 
10  grammes  of  dry  aluminum  sulphate,  A12(S04)3,  and  obtained  2.9934 
grammes  of  A1203  as  residue. 

Hence  Al  =  27.103. 

In  1835 1  Mather  published  a  single  analysis  of  aluminum  chloride, 
from  which  he  sought  to  fix  the  atomic  weight  of  the  metal.  0.646  grm. 
of  A1CL,  gave  him  2.056  of  AgCl  and  0.2975  of  A1203.  These  figures  give 
worthless  values  for  Al,  and  are  included  here  only  for  the  sake  of  com- 
pleteness. From  the  ratio  between  AgCl  and  A1C13,  Al  =  28.584. 

Tissier's  J  determination,  also  resting  on  a  single  experiment,  appeared 
in  1858.  Metallic  aluminum,  containing  .135  per  cent,  of  sodium,  was 
dissolved  in  hydrochloric  acid.  The  solution  was  evaporated  with  nitric 
acid  to  expel  all  chlorine,  and  the  residue  was  strongly  ignited  until  only 
alumina  remained.  1.935  grm.  of  Al  gave  3.645  grm.  of  A1.203.  If  we 
correct  for  the  trace  of  sodium  in  the  aluminum,  we  have  Al  =  26.930. 

Essentially  the  same  method  of  determination  was  adopted  by  Isnard,  § 
who,  although  not  next  in  chronological  order,  may  fittingly  be  men- 
tioned here.  He  found  that  9  grm.  of  aluminum  gave  17  grm.  of  A1.203. 
Hence  Al  =  26.8 

In  1858  Dumas,  1 1  in  connection  with  his  celebrated  revision  of  the 
atomic  weights,  made  seven  experiments  with  aluminum  chloride.  The 
material  was  prepared  in  quantity,  sublimed  over  iron  filings,  and  finally 
resublimed  from  metallic  aluminum.  Each  sample  used  was  collected 
in  a  small  glass  tube,  after  sublimation  from  aluminum  in  a  stream  of 
dry  hydrogen,  and  hermetically  enclosed.  Having  been  weighed  in  the 
tube,  it  was  dissolved  in  water,  and  the  quantity  of  silver  necessary  for 
precipitating  the  chlorine  was  determined.  Reducing  to  a  common 
standard,  his  weighings  give  the  quantities  of  A1C13  stated  in  the  third 
column,  as  proportional  to  100  parts  of  silver : 


1.8786  grm.  Alt 

.13  =4.543  grm.  Ag. 

41.352 

3.021               " 

7.292 

41.459—  Bad. 

2.399 

5.802 

41.348 

1.922               " 

4.6525       " 

41.311 

1.697 

4.1015 

4L375 

4-3165 

10.448         " 

4L3H 

6.728 

16.265 

41.365 

*Poggend.  Annal.,  8,  177. 

tSilliman's  Amer.  Journ.,  27,  241. 

J  Cotnpt.  Rend.,  46,  1105. 

I  Compt.  Rend.,  66,  508.     1868. 

||  Ann.  China.  Phys.  (3),  55,  151.    Ann.  Cheni.  Pharm.,  113,  26. 


ALUMINUM.  177 

In  the  second  experiment  the  A1C13  contained  traces  of  iron.  Reject- 
ing this  experiment,  the  remaining  six  give  a  mean  of  41.344,  ±  .007. 
These  data  give  a  value  for  Al  approximating  to  27.5,  and  were  for 
many  years  regarded  as  satisfactory.  It  now  seems  probable  that  the 
chloride  contained  traces  of  an  oxy-compound,  which  would  tend  to 
raise  the  atomic  weight. 

In  1879  Terreil  *  published  a  new  determination  of  the  atomic  weight 
under  consideration,  based  upon  a  direct  comparison  of  the  metal  with 
hydrogen.  Metallic  aluminum,  contained  in  a  tube  of  hard  glass,  was 
heated  strongly  in  a  current  of  dry  hydrochloric  acid.  Hydrogen  was 
set  free,  and  was  collected  over  a  strong  solution  of  caustic  potash. 
0.410  grm.  of  aluminum  thus  were  found  equivalent  to  508.2  cc.,  or 
.045671  grm.  of  hydrogen.  Hence  Al  =  26.932. 

About  a  year  after  Terrell's  determination  appeared,  the  lower  value 
for  aluminum  was  thoroughly  confirmed  by  J.  W.  Mallet.f  After  giving 
a  full  resume  of  the  work  done  by  others,  exclusive  of  Isnard,  the  author 
describes  his  own  experiments,  which  may  be  summarized  as  follows  : 

Four  methods  of  determination  were  employed,  each  one  simple  and 
direct,  and  at  the  same  time  independent  of  the  others.  First,  pure 
ammonia  alum  was  calcined,  and  the  residue  of  aluminum  oxide  was 
estimated.  Second,  aluminum  bromide  was  titrated  with  a  standard 
solution  of  silver.  Third,  metallic  aluminum  was  attacked  by  caustic 
soda,  and  the  hydrogen  evolved  was  measured.  Fourth,  hydrogen  was 
set  free  by  aluminum,  and  weighed  as  water.  Every  weight  was  care- 
fully verified,  the  verification  being  based  upon  the  direct  comparison, 
by  J.  E.  Hilgard,  of  a  kilogramme  weight  with  the  standard  kilogramme 
at  Washington.  The  specific  gravity  of  each  piece  was  determined,  and 
also  of  all  materials  and  vessels  used  in  the  weighings.  During  each 
weighing  both  barometer  and  thermometer  were  observed,  so  that  every 
result  represents  a  real  weight  in  vacuo. 

The  ammonium  alum  used  in  the  first  series  of  experiments  was 
specially  prepared,  and  was  absolutely  free  from  ascertainable  impuri- 
ties. The  salt  was  found,  however,  to  lose  traces  of  water  at  ordinary 
temperatures — a  circumstance  which  tended  towards  a  slight  elevation 
of  the  apparent  atomic  weight  of  aluminum  as  calculated  from  the 
weighings.  Two  sets  of  experiments  were  made  with  the  alum ;  one 
upon  a  sample  air-dried  for  two  hours  at  21°-25°,  the  other  upon  mate- 
rial dried  for  twenty-four  hours  at  19°-26°.  These  sets,  marked  A  and 
B  respectively,  differ  slightly,  B  being  the  less  trustworthy  of  the  two, 
judged  from  a  chemical  standpoint.  Mathematically  it  is  the  better  of 
the  two.  Calcination  was  effected  with  a  great  variety  of  precautions, 
concerning  which  the  original  memoir  must  be  consulted.  To  Mallet's 
weighings  I  append  the  percentages  of  A1203  deduced  from  them  : 

*  Bulletin  de  la  Soc.  Chimique,  31,  153. 
f  Phil.  Trans.,  1880,  p.  1003. 
12 


178  THE    ATOMIC    WEIGHTS. 

Series  A. 

8.2144  grm.  of  the  alum  gave    .9258  grm.  A12O3.  11.270  per  cent. 

14.0378  "  1.5825         "  11.273       " 

5.6201  "  '.6337          "  11.275       " 

11.2227  "  1.2657          "  11.278       " 

10.8435  "  1. 2216         "  11.266       " 

Mean,  11.2724,  ±  .0014 
Series  B. 

12.1023  grm.  of  the  alum  gave  1.3660  grm.  A12O3.  11.287  per  cent. 

10.4544  "  1.1796         "  11.283 

6.7962  "  .7670         "  11.286       " 

8.5601  "  .9654         "  11.278 

4.8992  .5528         "  11.283       " 

Mean,  n.,2834,  ±  .0011 

Combined,  these  series  give  a  general  mean  of  11.2793,  ±.  0008.  Hence 
Al  ===  26.952. 

The  aluminum  bromide  used  in  the  second  series  of  experiments  was 
prepared  by  the  direct  action  of  bromine  upon  the  metal.  The  product 
was  repeatedly  distilled,  the  earlier  portions  of  each  distillate  being  re- 
jected, until  a  constant  boiling  point  of  263. °3  at  747  mm.  pressure  was 
noted.  The  last  distillation  was  effected  in  an  atmosphere  of  pure  nitro- 
gen, in  order  to  avoid  the  possible  formation  of  oxide  or  oxy-bromide  of 
aluminum ;  and  the  distillate  was  collected  in  three  portions,  which 
proved  to  be  sensibly  identical.  The  individual  samples  of  bromide 
were  collected  in  thin  glass  tubes,  which  were  hermetically  sealed  after 
nearly  filling.  For  the  titration  pure  silver  was  prepared,  and  after 
fusion  upon  charcoal  it  was  heated  in  a  Sprengel  vacuum  in  order  to 
eliminate  occluded  gases.  This  silver  was  dissolved  in  specially  purified 
nitric  acid,  the  latter  but  very  slightly  in  excess.  The  aluminum  bro- 
mide, weighed  in  the  sealed  tube,  was  dissolved  in  water,  precautions  be- 
ing taken  to  avoid  any  loss  by  splashing  or  fuming  which  might  result 
from  the  violence  of  the  action.  To  the  solution  thus  obtained  the  silver 
solution  was  added,  the  silver  being  something  less  than  a  decigramme 
in  deficiency.  The  remaining  amount  of  silver  needed  to  complete  the 
precipitation  of  the  bromine  was  added  from  a  burette,  in  the  form  of  a 
standard  solution  containing  one  milligramme  of  metal  to  each  cubic 
centimetre.  The  final  results  were  as  follows,  the  figures  in  the  third 
column  representing  the  quantities  of  bromide  proportional  to  100  parts 
of  silver.  Series  A  is  from  the  first  portion  of  the  last  distillate  of  AlBr3 ; 
series  B  from  the  second  portion,  and  series  C  from  the  third  portion : 

Series  A. 

6.0024  grm.  AlBr3  =  7.2793  grm.  Ag.       82.458 
8.6492  10.4897    "         82.454 

3.1808'     "       3.8573    "         82.462 


ALUMINUM. 


179 


6.9617  grm.  AlBra 
11.2041      " 
3.7621 
5.2842 
9.7338 


Series  B. 

8.4429  grm 

13.5897 

4.5624 

6.4085 
11.8047 


Ag. 


82.456 
82.445 
82.459 
82.456 
82.457 


9-35I5  Srm- 

4.4426 

5.2750 


Series  C. 

AlBr3i=  1  1.  3424  grm.  Ag. 

5.3877 
"  6.3975 


82.447 
82.458 
82.454 

Mean,  82.455,  ±  .001 


Hence  Al  =  26.916. 

The  experiments  to  determine  the  amount  of  hydrogen  evolved  by  the 
action  of  caustic  soda  upon  metallic  aluminum  were  conducted  with  pure 
metal,  specially  prepared,  and  with  caustic  soda  made  from  sodium. 
The  soda  solution  was  so  strong  as  to  scarcely  lose  a  perceptible  amount 
of  water  by  the  passage  through  it  of  a  dry  gas  at  ordinary  temperature. 
As  the  details  of  the  experiments  are  somewhat  complex,  the  original 
memoir  must  be  consulted  for  them.  The  following  results  were  obtained, 
the  weight  of  the  hydrogen  being  calculated  from  the  volume,  reckoned 
at  .089872  gramme  per  litre. 


Wt.  AL 

•3697 
•3769 
.3620 

•  7579 
•73*4 

•7541 


Vol.  H. 
458.8 
467.9 
449-1 
941-5 
907.9 

936.4 


Wt.  H. 

.041234 
.042051 
.040362 
.084614 
.081595 
.084156 


At.  Wt. 

26.898 
26.889 
26.907 
26.872 
26.891 
26.882 


Mean,  26.890,  ±  .0034 


'he  closing  series  of  experiments  was  made  with  larger  quantities  of 
aluminum  than  were  used  in  the  foregoing  set.  The  hydrogen,  evolved 
by  the  action  of  the  caustic  alkali,  was  dried  by  passing  it  through  two 
drying  tubes  containing  pumice  stone  and  sulphuric  acid,  and  two  others 
containing  asbestos  and  phosphorus  pentoxide.  Thence  it  passed 
through  a  combustion  tube  containing  copper  oxide  heated  to  redness. 
A  stream  of  dry  nitrogen  was  employed  to  sweep  the  last  traces  of  hy- 
drogen into  the  combustion  tube,  and  dry  air  was  afterwards  passed 
through  the  entire  apparatus  to  reoxidize  the  surface  of  reduced  copper, 
and  to  prevent  the  retention  of  occluded  hydrogen.  The  water  formed 
by  the  oxidation  of  the  hydrogen  was  collected  in  three  drying  tubes. 


180  THE   ATOMIC   WEIGHTS. 

The  results  obtained  were  as  follows.     The  third  column  gives  the  amount 
of  water  formed  from  10  grammes  of  aluminum. 

2.1704  grm.  Al  gave  2.1661  grm.  H2O.  9.9802 

2.9355  "  2.9292         «  9-9785 

5.2632  "  5-2562         "  9-9867 

Mean,  9.9818,  ±  .0017 

Hence  Al  =  26.867. 

From  the  last  two  series  of  experiments  an  independent  value  for  the 
atomic  weight  of  oxygen  may  be  calculated.  It  becomes  O  =  15.895. 
The  closeness  of  this  figure  to  some  of  the  best  determinations  affords  a 
good  indication  of  the  accuracy  of  Mallet's  work. 

In  connection  with  Mallet's  work  it  is  worth  noting  that  Torrey  *  pub- 
lished a  series  of  measurements  of  the  H  :  Al  ratio,  representing  determi- 
nations made  under  his  direction  by  elementary  students.  These  meas- 
urements are  thirteen  in  number,  and  calculated  with  Regnault's  old 
value  for  the  weight  of  hydrogen,  range  from  26.661  to  27.360,  or  in  mean, 
27.049,  ±  .323.  Corrected  by  the  latest  value  for  the  weight  of  H,  this 
mean  becomes  26.967.  The  result,  of  course,  has  only  confirmatory 
significance. 

By  Baubignyf  we  have  only  two  determinations,  based  upon  the 
calcination  of  anhydrous  aluminum  sulphate,  A12(SOJ3. 

3.6745  grm.  salt  gave  1.0965  A12O3.  29.841  per  cent. 

2.539  "  -7572      "  29.823      " 

Mean,  29.832,  ±  .0061 

Hence  Al  =  26.858. 

It  is  clear  that  the  single  determinations  of  Berzelius,  Mather,  Tissier, 
Isnard,  and  Terrell  may  now  be  safely  left  out  of  account,  for  the  reason 
that  none  of  them  could  affect  appreciably  the  final  value  for  Al.  The 
ratios  to  consider  are  as  follows : 

(I.)  3Ag  :  A1C13  :  :  TOO  :  41. 344,  ±  .0070 

(2.)  Percentage  of  A12O3  in  ammonium  alum,  11.2793,  rb  .0008 

(3-)  3^g  :  A113r3  :  :  100  :  82.455,  ±  .0010 

(4.)  H  :  Al  :  :  I  :  26.890,  ±  .0034 

(5-)  A12  :  3H2O  :  :  10  :  9.9818,  ±  .0017 

(6.)  Percentage  of  A12O3  in  A12(SO4)3,  29.832,  ±  .0061 

The  antecedent  values  are — 

O    =    15.879,43.0003  Br=    79-344,  ±  .0062 

Ag=  107.108,  ±  .0031  N=    13.935,  d=.oo2i 

Cl  =    35.179,  ±  .0048  S   ==    31.828,  ±  .0015 

*  Am.  Chem.  Journ.,  10,  74.     1888. 
f  Compt.  Rend.,  97,  1369.     1883. 


GALLIUM.  181 

Hence  for  aluminum  we  have — 

From  (i) Al  =  27.31 1,  ±  .0270 

From  (2) "  =  26.952,  db  .0037 

From  (3) "  =  26.916,  ±  .0201 

From  (4) "  =  26.890,  rh  .0034 

From  (5) "  =  26.867,  ±  .0046 

From  (6) "  =  26.858,  ±  .0113 

General  mean Al  =  26.906,  ±  .0021 

With  0  =  16,  Al  =  27.111.     The  rejection  of  Dumas'  data  only  lowers 
the  result  to  26.903. 


GALLIUM. 

Gallium  has  been  so  recently  discovered,  and  obtained  in  such  small 
quantities,  that  its  atomic  weight  has  not  as  yet  been  determined  with 
much  precision.  The  following  data  were  fixed  by  the  discoverer, 
Lecoq  de  Boisbaudran  :  * 

3.1044  grammes  gallium  ammonium  alum,  upon  ignition,  left  .5885 
grm.  Ga.2O3. 

Hence  Ga  =  69.595.     If  0  =  16,  Ga  =  70.125. 

.4481  grammes  gallium,  converted  into  nitrate  and  ignited,  gave 
.6024  grm.  Ga2O3. 

Hence  Ga  =  69.171.     If  O  =  16,  Ga  =  69.698. 

These  values,  assigned  equal  weight,  give  these  means  : 

With  H  =  i,  Ga  =  69.383.  With  O  =  16,  Ga  =  69.912 

*  Journ.  Chem.  Soc.,  1878,  p.  646. 


182  THE   ATOMIC    WEIGHTS. 


INDIUM. 

Reich  and  Richter,  the  discoverers  of  indium,  were  also  the  first  to 
determine  its  atomic  weight.*  They  dissolved  weighed  quantities  of  the 
metal  in  nitric  acid,  precipitated  the  solution  with  ammonia,  ignited  the 
precipitate,  and  ascertained  its  weight.  Two  experiments  were  made,  as 
follows : 

•5T35  Srm-  indium  gave  .6243  grm.  In2O3. 
.699       «       .8515 

Hence,  in  mean,  In  =  110.61,  if  0  =  16 ;  a  value  known  now  to  he 
too  low. 

An  un weighed  quantity  of  fresh,  moist  indium  sulphide  was  also  dis- 
solved in  nitric  acid,  yielding,  on  precipitation, 

.2105  grm.  In2O3  and  .542  grm.  BaSO4. 

Hence,  with  BaS04  =  233.505,  In  =  112.03 ;  also  too  low. 

Soon  after  the  publication  of  Reich  and  Richter's  paper  the  subject 
was  taken  up  by  Winkler  .f  He  dissolved  indium  in  nitric  acid,  evap- 
orated to  dryness,  ignited  the  residue,  and  weighed  the  oxide  thus 
obtained. 

•5574  Srm-  I*1  gave  .6817  Srm-  In2O3. 
.6661     "     .8144    " 
.5011      "     .6126    " 

Hence,  in  mean,  if  0  =  16,  In  =  107.76  ;  a  result  even  lower  than  the 
values  already  cited. 

In  a  later  paper  by  Winkler  J  better  results  were  obtained.  Two 
methods  were  employed.  First,  metallic  indium  was  placed  in  a  solu- 
tion of  pure,  neutral,  sodio-auric  chloride,  and  the  amount  of  gold  pre- 
cipitated was  weighed.  I  give  the  weighings  and,  in  a  third  columnr 
the  amount  of  indium  proportional  to  100  parts  of  gold  : 

In.  Au.  Ratio. 

.4471  grm.  .8205  grm.  57-782 

.8445     «  1.4596    "  57.858 

Mean,  57.820,  ±  .026 

Hence,  if  Au  =  195.743,  ±  .0049,  In  =  113.179,  ±  .0517. 
Winkler  also  repeated  his  earlier   process,  converting  indium  into 
oxide  by  solution  in  nitric  acid  and  ignition  of  the  residue.     An  ad- 

*  Journ.  fur  Prakt.  Chem.,  92,  484. 
t  Journ.  fur  Prakt.  Chem.,  94,  8. 
%  Journ.  fur  Prakt.  Chem.,  102,  282. 


INDIUM.  183 

ditional  experiment,  the  third  as  given  below,  was  made  after  the  method 
of  Reich  and  Richter.     The  third  column  gives  the  percentage  of  In  in 

In203: 

1.124  grm-  Jn  gave  1.3616  grm.  In2O3.  Per  cent.,  82.550 

1.015  "             1.2291          "  "         82.581 

.6376  "               .7725          «  »         82.537 

These  figures  were  confirmed  by  a  single  experiment  of  Bunsen's,* 
published  simultaneously  with  the  specific  heat  determinations  which 
showed  that  the  oxide  of  indium  was  In203,  and  not  InO,  as  had  been 
previously  supposed : 

1.0592  grm.  In  gave  1.2825  grm.  In2O3.      Per  cent.  In,  82.589 

For  convenience  we  may  add  this  figure  in  with  Winkler's  series,  which 
gives  us  a  mean  percentage  of  In  in  In20s  of  82.564,  ±  .0082.  Hence,  if 
0  =  15.879,  ±  .0003,  In  =  112.787,  ±  .0542. 

Combining  both  values,  we  have — 

From  gold  series In  =  113.179,  =b  .0517 

From  oxide  series '.    ((  =  112.787,  ±  .0542 


General  mean In  =  1 12.992,  ±  .0374 

If  0  =  16,  In  =  113.853. 

*  Poggend.  Annal.,  141,  28. 


184 


THE    ATOMIC    WEIGHTS. 


THALLIUM. 

The  atomic  weight  of  this  interesting  metal  has  been  fixed  by  the  re- 
searches of  Lamy,  Werther,  Hebberling,  Crookes,  and  Lepierre. 

Lamy  and  Hebberling  investigated  the  chloride  and  sulphate  ;  Wer- 
ther studied  the  iodide;  Crookes'  experiments  involved  the  synthesis  of 
the  nitrate.  Lepierre's  work  is  still  more  recent,  and  is  based  upon 
several  compounds. 

Lamy  *  gives  the  results  of  one  analysis  of  thallium  sulphate  and  three 
of  thallium  chloride.  3.423  grammes  T12S04  gave  1.578  grm.  BaS04; 
whence  100  parts  of  the  latter  are  equivalent  to  216.920  of  the  former. 
In  the  thallium  chloride  the  chlorine  was  estimated  as  silver  chloride. 
The  following  results  were  obtained.  In  the  third  column  I  give  the 
amount  of  T1C1  proportional  to  100  parts  of  AgCl : 

3.912  grm.  T1C1  gave  2.346  grm.  AgCl.  166.752 

3.000  "  1.8015         u  166.528 

3.912  "  2.336  "  167.466 

Mean,  166.915,  ±.1905 

Hebberling's  f  work  resembles  that  of  Lamy.  Reducing  his  weighings 
to  the  standards  adopted  above,  we  have  from  his  sulphate  series,  as 
equivalent  to  100  parts  of  BaS04,  the  amounts  of  T1,S04  given  in  the 
third  column  : 

1.4195  grm.  T12SO4  gave  .6534  grm.  BaSO4.  217.248 

1.1924  "  .5507          "  216.524 

.8560  "  .3957          "  216.325 


Mean,  216.699 

Including  Lamy's  single  result  as  of  equal  weight,  we  get  a  mean  of 
216.754,  ±  .1387. 

From  the  chloride  series  we  have  these  results,  with  the  ratio  stated 
as  usual : 

.2984  grm.  T1C1  gave  .1791  grm.  AgCl.  166.611 

.5452  "  .3278          "  166.321 

Mean,  166,465,  =b  .097 

Lamy's  mean  was  166.915,  ±  .1905.  Both  means  combined  give  a 
general  mean  of  166.555,  ±  .0865. 

Werther'sJ  determinations  of  iodine  in  thallium  iodide  were  made  by 
two  methods.  In.  the  first  series  Til  was  decomposed  by  zinc  and  potas- 
sium hydroxide,  and  in  the  filtrate  the  iodine  was  estimated  as  Agl. 

*Zeit.  Anal.  Chem.,  2,  211.     1863. 
f  Ann.  Chem.  Pharm.,  134,  n.     1865. 
%  Journ.  fur  Prakt.  Chem.,  92,  128.     1864. 


THALLIUM.  185 

One  hundred  parts  of  Agl  correspond  to  the  amounts  of  Til  given  in 
the  last  column : 

.720  grm.  Til  gave    .51    grm.  Agl.  141.176 

2.072  "  1.472         "  140.761 

.960  "  .679         "  141-384 

•385  -273         "  141.026 

1.068  "  .759         "  140.711 


Mean,  141.012,  ±  .085 

In  the  second  series  the  thallium  iodide  was  decomposed  by  ammonia 
in  presence  of  silver  nitrate,  and  the  resulting  Agl  was  weighed.  Ex- 
pressed according  to  the  foregoing  standard,  the  results  are  as  follows  : 

1.375  grm.  Til  gave    .978  grm.  Agl.  Ratio,  140.593 

1.540  1.095          "  "       140.639 

1.380  "  .981          "  "       140.673 

Mean,  140.635,  db  .016 

General  mean  of  both  series,  140.648,  ±  .016. 

In  1873  Crookes,*  the  discoverer  of  thallium,  published  his  final  deter- 
mination of  its  atomic  weight.  His  method  was  to  effect  the  synthesis  of 
thallium  nitrate  from  weighed  quantities  of  absolutely  pure  thallium. 
No  precaution  necessary  to  ensure  purity  of  materials  was  neglected  ;  the- 
balances  were  constructed  especially  for  the  research ;  the  weights  were 
accurately  tested  and  all  their  errors  ascertained ;  weighings  were  made 
partly  in  air  and  partly  in  vacuo,  but  all  were  reduced  to  absolute  stand- 
ards ;  and  unusually  large  quantities  of  thallium  were  employed  in  each 
experiment.  In  short,  no  effort  was  spared  to  attain  as  nearly  as  possi- 
ble absolute  precision  of  results.  The  details  of  the  investigation  are  too 
voluminous,  however,  to  be  cited  here ;  the  reader  who  wishes  to  become 
familiar  with  them  must  consult  the  original  memoir.  Suffice  it  to  say 
that  the  research  is  a  model  which  other  chemists  will  do  well  to  copy. 

The  results  of  ten  experiments  by  Professor  Crookes  may  be  stated  as 
follows.  In  a  final  column  I  give  the  quantity  of  nitrate  producible 
from  100  parts  of  thallium.  The  weights  given  are  in  grains  : 


Thallium. 

TINO^  +  Glass. 

Glass  Vessel. 

Ratio. 

497.972995 

1121.851852 

472.557319 

130.3875 

293.193507 

i  i  11.387014 

729.082713 

130.393° 

288  562777 

971.214142 

594.949719 

130.3926 

324.963740 

1142.569408 

718.849078 

1  30.  3900 

183.790232 

1005.779897 

766.133831 

130.3912 

190.842532 

997.334615 

748.491271 

130.3920 

195.544324 

1022.176679 

767.203451 

I30-39I5 

201.816345 

1013.480135 

750.332401 

130.3897 

295.683523 

H53.947672 

768.403621 

130.3908 

299.203036 

1159.870052 

769.734201 

130.3917 

Mean, 

130.3910,  ±  .00034 

*  Phil.  Trans.,  1873,  p.  277. 


186  THE    ATOMIC    WEIGHTS. 

Lepierre's*  determinations  were  published  in  1893,  and  represented 
several  distinct  methods.  First,  thallous  sulphate  was  subjected  to  elec- 
trolysis in  presence  of  an  excess  of  ammonium  oxalate,  the  reduced 
metal  being  dried  and  weighed  in  an  atmosphere  of  hydrogen.  The  cor- 
rected weights,  etc.,  are  as  follows: 

J-8935  grm.  T12SO4  gave  1.5327  Tl.  80.945  per  cent. 

2.7243  "  2.2055    "  80.957 

2.8112  "  2.2759    "  80.958       " 


Mean,  80.953,  =t  .0030 

Secondly,  weighed  quantities  of  crystallized  thallic  oxide  were  con- 
verted into  thallous  sulphate  by  means  of  sulphurous  acid,  and  the  solu- 
tion was  then  subjected  to  electrolysis,  as  in  the  preceding  series. 

3.2216  grm.  T12O8  gave  2.8829  Tl.  89.487  per  cent. 

2.5417  "  2.2742    "  89.475 

Mean,  89.481,  =h  .0040 

In  the  third  set  of  experiments  a  definite  amount  of  thallous  sulphate 
or  nitrate  was  fused  in  a  polished  silver  crucible  with  ten  times  its  weight 
of  absolutely  pure  caustic  potash.  Thallic  oxide  was  thus  formed,  which, 
with  various  precautions,  was  washed  with  water  and  alcohol,  and  finally 
weighed  in  the  original  crucible.  One  experiment  with  the  nitrate  gave — 

2.7591  grm.  T1NO3  yields  2.3649  T12O3.  85.713  per  cent. 

Two  experiments  were  made  with  the  sulphate,  as  follows : 

3.1012  grm.  T12SO4  gave  2.8056  T12O3.  90.468  per  cent. 

2.3478  "  2.1239      "  90-463       " 

Mean,  90.465,  ±  .0020 

Finally,  crystallized  thallic  oxide  was  reduced  by  heat  in  a  stream  of 
hydrogen,  and  the  water  so  formed  was  collected  and  weighed. 

2.7873  grm.  T12O3  gave  .3301  H2O.  11.843  Per  cent- 

3.9871  "  .4716     "  11.828       " 

4.0213  "  .4761     "  11-839       " 


Mean,  11.837,  d=  .0029 

Iii  a  supplementary  notef  Lepierre  states  that  his  weights  were  all 
reduced  to  vacuum  standards. 

Some  work  by  Wells  and  Penfield,  J  incidentally  involving  a  deter- 
mination of  atomic  weight,  but  primarily  intended  for  another  purpose, 
may  also  be  taken  into  account.  Their  question  was  as  to  the  constancy 
of  thallium  itself.  The  nitrate  was  repeatedly  crystallized,  and  the  last 
crystallization,  with  the  mother  liquor  representing  the  opposite  end  of 

*  Bull.  Soc.  Chim.  (3),  9,  166. 
fBull.  Soc.  Chim.  (3),  n,  423.     1894. 
J  Amer.  Journ.  Sci.  (3),  47,  466.     1894. 


THALLIUM.  187 

the  series,  were  both  converted  into  chloride.  In  the  latter  the  chlorine 
was  estimated  as  silver  chloride,  which  was  wreighed  on  a  Gooch  filter, 
with  the  results  given  below,  which  are  sensibly  identical.  The  T1C1 
equivalent  to  100  parts  of  AgCl  is  stated  in  the  last  column. 

TICl.  AgCl.  Ratio. 

Crystals 3-9*46  2.3393  167.341 

Mother  liquor 3-34'5  1.9968  167. 343 

Mean,  167.342 

The  general  mean  of  Lamy's  and  Hebberling's  determinations  of  this 
ratio  gave  166.555,  ±:  .0865.  If  we  arbitrarily  assign  Wells  and  Pen- 
field's  mean  equal  weight  with  that,  we  get  a  new  general  mean  of 
166.948,  ±  .0610. 

The  ratios  to  be  considered  are  now  as  follows : 

(I.)   BaSO4  :  T12SO4  :  :  100  :  216.754,  ±  .1387 
(2.)  AgCl  :  TICl  :  :  100  :  166.948,  ±  .0610 
(3.)   Agl  :  Til  :  :  100  :  140.648,  ±  .016 
(4.)  Tl  :  T1NO3  :  :  100  :  130.391,  +  .00034 
(5.)   T12S04  :  T12  :  :  100  :  80.953,  ±  .0030 
(6.)  T12O3  :  T12  :  :  IOO  :  89.481,  ±  .0040 
(7.)   2T1N03  :  T1203  :  :  100:85.713 
(8.)  T12SO4  :  T12O3  :  :  100  :  90.465,  ±  .0020 
(9.)  T12O3  :  3H2O  :  :  IOO  :  11.837,  ±  .0029 

And  the  antecedent  data  are  these  : 

0  =  15.879,  db  .0003  N   =  13.935,  db  .0021 
Ag=  107.108,  =b  .0031  S    =  31.828,  it  .0015 
Cl  =  35.179,  =fc  .0048  AgCl  =  142.287,  i  .0037 

1  =  125.888,  ±  .0069  Agl  =  232.996,  db  .0062 

Ratio  number  seven  rests  upon  a  single  experiment,  and  the  atomic 
weight  of  thallium  derived  from  it  must  therefore  be  arbitrarily  weighted. 
It  has  been  assumed,  therefore,  that  its  probable  error  is  the  same  as  that 
from  number  eight.  Taking  this  much  for  granted,  we  have  nine  values 
for  thallium,  as  given  below  : 

From  (i) Tl  =  203.478,  ±  .1610 

Fro'm  (2) "  =  202.366,  db  .0872 

From  (3) "  =  201.816,  ±  .0389 

From  (4) ' '  =  202. 595,  ±.0117 

From  (5) "  =  202.614,  ±  .0330 

From  (6) "  =  202  620,  ±  .0775 

From  (7) "  =  202.679,  d=  .0483 

From  (8) "  =  202.496,  ±  .0483 

From  (9) '*  =  202.746,  d=  .0576 

General  mean Tl  =  202.555,  ±  .0098 

If  0  =  16,  Tl  =  204.098. 


188  THE   ATOMIC    WEIGHTS. 

If  we  reject  the  first  three  values,  retaining  only  those  due  to  the  ex- 
periments of  Crookes  and  Lepierre,  we  have — 

Tl  =  202.605,  ±  .0103 

If  O  =  16,  this  becomes  204.149.  This  mean  exceeds  Crookes'  deter- 
mination only  by  0.01,  and  may  be  regarded  as  fairly  satisfactory. 
Crookes'  ratio  evidently  outweighs  all  the  others. 


SILICON. 

Although  Berzelius  *  attempted  to  ascertain  the  atomic  weight  of 
silicon,  first  by  converting  pure  Si  into  Si02,  and  later  from  the  analysis 
of  BaSiF6,  his  results  were  not  satisfactory.  We  need  consider  only  the 
work  of  Pelouze,  Schiel,  Dumas,  and  Thorpe  and  Young. 

Pelouze,f  experimenting  upon  silicon  tetrachloride,  employed  his 
usual  method  of  titration  with  a  solution  containing  a  known  weight  of 
silver.  One  hundred  parts  of  Ag  gave  the  following  equivalencies  of 
SiCl4 : 

39-4325 
39.4570 


Mean,  39.4447,  ±  .0083 

Essentially  the  same  method  was  adopted  by  Dumas.  J  Pure  SiCl4 
was  weighed  in  a  sealed  glass  bulb,  then  decomposed  by  water,  and 
titrated.  The  results  for  100  Ag  are  given  in  the  third  column  : 

2.899  grm.  SiCl4  =  7.3558  grm.  Ag.  39.41 1 

1.242  "  3.154          "  39-379 

3.221  8.1875         "  39.340 

Mean,  39.377,  db  .014 

Dumas'  and  Pelouze's  series  combine  as  follows  : 

Pelouze 39.4447,  dr  .0083 

Dumas 39.377,    ±  .014 

General  mean 39.4265,  =fc  .0071 

Schiel,  §  also  studying  the  chloride  of  silicon,  decomposed  it  by  am- 
monia. After  wanning  and  long  standing  it  was  filtered,  and  in  the 

*  Lehrbuch,  5  Aufl.,  3,  1200. 
f  Compt.  Rend.,  20,  1047.     1845. 
I  Ann.  Cheni.  Pharm.,  113,  31.     1860. 
§Ann.  Chem.  Pharm.,  120,94. 


SILICON.  189 

filtrate  the  chlorine  was  estimated  as  AgCl.     One  hundred  parts  of  AgCl 
correspond  to  the  quantities  of  SiCl4  given  in  the  last  column  : 

.6738  grm.  SiCl4  gave  2.277  grm-  AgCl.  29.592 

1.3092  "  4.418          "  29.633 


Mean,  29.6125,  ±  .0138 

Thorpe  and  Young,*  working  with  silicon  bromide,  seem  to  have  ob- 
tained fairly  good  results.  The  bromide  was  perfectly  clear  and  color- 
less, and  boiled  constantly  at  153°.  It  was  weighed,  decomposed  with 
water,  and  evaporated  to  dryness,the  crucible  containing  it  being  finally 
ignited.  The  crucible  was  tared  by  one  precisely  similar,  in  which  an 
equal  volume  of  water  was  also  evaporated.  Results  as  follows,  with 
weights  at  vacuum  standards : 

9.63007  grm.  SiBr4  gave  1.67070  SiO2.  17.349  per  cent. 

12.36099  "  2.14318  "  17.338 

12.98336  2.25244  "  17-349  " 

9.02269  "  L56542  "  I7-350  " 

15.38426  "  2.66518  "  17.324  " 

9.74550  1.69020  "  17-343 

6.19159  "  1.07536  "  17.368  " 

9.51204  "  1.65065  "  17.353  " 

10.69317  1.85555  "  '7-353  " 

Mean,  17.347,  ±.0027 

The  ratios  now  available  are — 

(i.)  4Ag  :  SiCl4  :  :  100  :  39.4265,  ±  .0071 
(2.)  4AgCl  :  SiCl4  :  :  100  :  29.6125,  =b  .0138 
(3.)  SiBr4  :  SiO2  :  :  loo  :  17.347,  ±  .0027 

Reducing  these  ratios  with — 

O  =  I5-879,  db  .0003  Br  =  79.344,  ±  .0062 
Ag=  107.108,  ±  .0031  AgCl  =  142.287,  ±  .0037, 
Cl  =.  35.179,  =h  .0048 

we  have  the  following  values  for  the  atomic  weight  of  silicon  : 

From  (i) Si  =  28.200,  ±  .0363 

From  (2) "  =  27.823,  ±  .0810 

From  (3) ....    "  =  28.187,  =b  .0122 


General  mean Si  —  28.181,  ±  .0114 

If  0  =  16,  Si  =  28.395. 

*Journ.  Chem.  Soc.,  51,576.     1887. 


190  THE    ATOMIC    WEIGHTS. 


TITANIUM. 

The  earliest  determinations  of  the  atomic  weight  of  titanium  are  due 
to  Heinrich  Rose.*  In  his  first  investigation  he  studied  the  conversion 
of  titanium  sulphide  into  titanic  acid,  and  obtained  erroneous  results ; 
later,  in  1829,  he  published  his  analyses  of  the  chloride,  f  This  compound 
was  purified  by  repeated  rectifications  over  mercury  and  over  potassium, 
and  was  weighed  in  bulbs  of  thin  glass.  These  were  broken  under  water 
in  tightly  stoppered  flasks ;  the  titanic  acid  was  precipitated  by  ammo- 
nia, and  the  chlorine  was  estimated  as  silver  chloride.  The  following 
results  were  obtained.  In  a  fourth  column  I  give  the  Ti02  in  percentages 
referred  to  TiCl4  as  100,  and  in  a  fifth  column  the  quantity  of  TiCl4  pro- 
portional to  100  parts  of  AgCl : 

TiCl±.  TiOT  AgCl.  Percent.  TiO.2.  AgCl  Ratio. 

.885    grm.          .379  grm.  2.661  grm.  42.825  33-2S8 

2.6365     "  1. 120    "  7.954    "  42.481  33-147 

I.7I57     "  -732    "  5-I72    "  42.665  33.173 

3.0455    "  1.322    "  9.198    "  43.423  33-100 

2.4403     "  1.056    '  7.372     "  43-273  33.102 

Mean,  42.933,  ±  .121         33.156,  ±.019 

If  we  directly  compare  the  AgCl  with  the  Ti02  we  shall  find  100  parts 
of  the  former  proportional  to  the  following  quantities  of  the  latter : 

14.243 
14.081 
14-153 
H.373 
14.324 


Mean,  14.235,  ±  .036 

Shortly  after  the  appearance  of  Rose's  paper,  MosanderJ  published 
some  figures  giving  the  percentage  of  oxygen  in  titanium  dioxide,  from 
which  a  value  for  the  atomic  weight  of  titanium  was  deduced.  Although 
no  details  are  furnished  as  to  experimental  methods,  and  no  actual  weigh- 
ings are  given,  I  cite  his  percentages  for  whatever  they  may  be  worth  : 

40.814 

40.825 

40.610 

40. 1 80 

40.107 

40.050 

40.780 

40.660 

39-830 

Mean,  40.428 

*  Gilbert's  Annalen,  1823,  67  and  129. 

t  Poggend.  Annalen,  15,  145.     Berz.  I,ehrbuch,  3,  1210. 

j  Berz.  Jahresbericht,  10,  108.     1831. 


TITANIUM.  191 

These  figures,  with  O  =  15.879,  give  values  for  Ti  ranging  from  46.03 
to  47.98;  or,  in  mean,  Ti  =  46.80.  They  are  not,  however,  sufficiently 
explicit  to  deserve  any  farther  consideration. 

In  1847  Isidor  Pierre  made  public  a  series  of  important  determina- 
tions.* Titanium  chloride,  free  from  silicon  and  from  iron,  was  pre- 
pared by  the  action  of  chlorine  upon  a  mixture  of  carbon  with  pure, 
artificial  titanic  acid.  This  chloride  was  weighed  in  sealed  tubes,  these 
were  broken  under  water,  and  the  resulting  hydrochloric  acid  was  titrated 
with  a  standard  solution  of  silver  after  the  method  of  Pelouze.  I  subjoin 
Pierre's  weighings,  and  add,  in  a  third  column,  the  ratio  of  TiCl4  to  100 
parts  of  silver  : 

TiClt.  Afr.  Ratio. 

.8215  grm.  1.84523  gran.  44-52° 

.7740  "  i.73909  "  44-506 

•  7775  "  I.746I3  "  44.527 

.7160  "  1.61219  "  44412 

.8085  "  1.82344  "  44-339 

.6325  "  1.42230  "  44.470 

•8155  "  1-83705  "  44-39.2 

.8165  «  1.83899  "  44.399 

.8065  "  1.81965  "  44.322 


Mean,  44.432,  ±  .0173 

It  will  be  seen  that  the  first  three  of  these  results  agree  well  with  each 
other  and  are  much  higher  than  the  remaining  six.  The  last  four  ex- 
periments were  made  purposely  with  tubes  which  had  been  previously 
opened,  in  order  to  determine  the  cause  of  the  discrepancy.  According 
to  Pierre,  the  opening  of  a  tube  of  titanium  chloride  admits  a  trace  of 
atmospheric  moisture.  This  causes  a  deposit  of  titanic  acid  near  the 
mouth  of  the  tube,  and  liberates  hydrochloric  acid.  The  latter  gas  being 
heavy,  a  part  of  it  falls  back  into  the  tube,  so  that  the  remaining  chloride 
is  richer  in  chlorine  and  poorer  in  titanium  than  it  should  be.  Hence, 
upon  titration,  too  low  figures  for  the  atomic  weight  of  titanium  are 
obtained.  Pierre  accordingly  rejects  all  but  the  first  three  of  the  above 
estimations. 

The  memoir  of  Pierre  upon  the  atomic  weight  of  titanium  was  soon 
followed  by  a  paper  from  Demoly,  f  who  obtained  much  higher  results. 
He  also  started  out  from  titanic  chloride,  which  was  prepared  'from  rutile. 
The  latter  substance  was  found  to  contain  1.8  per  cent,  of  silica  ;  whence 
Demoly  inferred  that  the  TiCl4  investigated  by  Rose  and  by  Pierre  might 
have  been  contaminated  with  SiCl4,  an  impurity  which  would  lower  the 
value  deduced  for  the  atomic  weight  under  consideration.  Accordingly, 
in  order  to  eliminate  all  such  possible  impurities,  this  process  was  resorted 

*Ann.  Chim.  Phys.  (3),  20,  257. 

t  Ann.  Chem.  Pharm.,  72,  214.     1849. 


192  THE    ATOMIC    WEIGHTS. 

to  :  the  chloride,  after  rectification  over  mercury  and  potassium,  was 
acted  upon  by  dry  ammonia,  whereupon  the  compound  TiCl4.4NH3  was 
deposited  as  a  white  powder.  This  was  ignited  in  dry  ammonia  gas,  and 
the  residue,  by  means  of  chlorine,  was  reconverted  into  titanic  chloride, 
which  was  again  repeatedly  rectified  over  mercury,  potassium,  and  po- 
tassium amalgam.  The  product  boiled  steadily  at  135°.  This  chloride, 
after  weighing  in  a  glass  bulb,  was  decomposed  by  water,  the  titanic  acid 
was  precipitated  by  ammonia,  and  the  chlorine  was  estimated  in  the 
filtrate  as  silver  chloride.  Three  analyses  were  performed,  yielding  the 
following  results.  I  give  the  actual  weighings  : 

1.470  grm.  TiCl4  gave  4.241  grm.  AgCl  and  .565  grm.  TiO2 
2.330  "  6.752  .801          " 

2.880  "  8.330  "  1.088          " 

The  ".801  "  in  the  last  column  is  certainly  a  misprint  for  .901.     Assum- 
ing this  correction,  the  results  may  be  given  in  three  ratios,  thus  : 


Per  cent.  TiOifrom  TiClv  TiCl±:  looAgCl.  TiO2  :  woAgCL 

38.435  34-662  13-322 

38669  34.  508  13.344 

37.778  34-574  13.061 


Mean,  38.294,  ±  .180  34-58i,  ±  .030  13.242,  zfc  .061 

These  three  ratios  give  three  widely  divergent  values  for  the  atomic 
weight  of  titanium,  ranging  from  about  36  to  more  than  56,  the  latter 
figure  being  derived  from  the  ratio  between  AgCl  and  TiCl4.  This  value, 
56,  is  assumed  by  Demoly  to  be  the  best,  the  others  being  practically 
ignored. 

Upon  comparing  Demoly's  figures  with  those  obtained  by  Rose,  certain 
points  of  similarity  are  plainly  to  be  noted.  Both  sets  of  results  were 
reached  by  essentially  the  same  method,  and  in  both  the  discordance 
between  the  percentages  of  titanic  acid  and  of  silver  chloride  is  glaring. 
This  discordance  can  rationally  be  accounted  for  by  assuming  that  the 
titanic  chloride  was  in  neither  case  absolutely  what  it  purported  to  be ; 
that,  in  brief,  it  must  have  contained  impurities,  such  for  example  as 
hydrochloric  acid,  as  shown  in  the  experiments  of  Pierre,  or  possibly 
traces  of  oxy chlorides.  Considerations  of  this  kind  also  throw  doubt 
upon  the  results  attained  by  Pierre,  for  he  neglected  the  direct  estimation 
of  the  titanic  acid  altogether,  thus  leaving  us  without  means  for  correctly 
judging  as  to  the  character  of  his  material. 

In  1883*  Thorpe  published  a  series  of  experiments  upon  titanium 
tetrachloride,  determining  three  distinct  ratios  and  getting  sharply  con- 
cordant results.  The  first  ratio,  which  was  essentially  like  Pierre's,  by 

*  Berichte  Deutsch.  Chem.  Gesell.,  16,  3014.     1883. 


TITANIUM.  193 

decomposition  with  water  and  titration  with  silver,  was  in  detail  as 
follows : 


7VC/4. 

Ag. 

7VC74  :  iooAg. 

2-43275 

5.52797 

44.008 

5-42332 

12.32260 

44.015 

3.59601 

8.17461 

44.000 

3.31222 

7.52721 

44.003 

4.20093 

9.54679 

44.004 

5.68888 

12.92686 

44.008 

5.65346 

12.85490 

43-979 

4.08247 

9.28305 

43.978 

Mean,  43.999,  =b  .0032 
Pierre  found,  44.432,  d=  .0073 

General  mean,  44.017,  db  .0031 

The  second  ratio,  which  involved  the  weights  of  TiCl4  taken  in  the  last 
five  determinations  of  the  preceding  series,  included  the  weighing  of  the 
silver  chloride  formed.  The  TiCl4  proportional  to  100  parts  of  AgCl  is 
given  in  a  third  column  : 

7Ya4.  AgCl.  Ratio. 

3.31222  10.00235  33- "4 

4.20093  12.68762  33.111 

5.68888  17.17842  33.117 

5.65346  17.06703  33-I25 

4.08247  12.32442  33-I25 

Mean,  33.118,  ±  .0019 
Rose  found,  33.156,  =b  .019 
Demoly  found,  34.581,  ±  .030 


General  mean,  33.123,  ±  .0019. 

In  the  third  series  the  chloride  was  decomposed  by  water,  and  after 
evaporation  to  dry  ness  the  resulting  Ti02  was  strongly  ignited. 

TtC/t.  TiOv                       Percent.  TiO.,. 

6.23398  2.62825  42.160 

8.96938  3./8335  42.181 

10.19853  4.30128  42.176 

6.56894  2.77011  42.170 

8.99981  3-79575  42.176 

8.32885  3-5"58  42.162 


Mean,  42.171,  ±  .0022 
Rose  found,  42.933,  dr  .121 
Demoly  found,  38.294,  ±  .180 


General  mean,  42.171,  ±  .0022 

In  short,  the  work  of  Rose,  Pierre,  and  Demoly  practically  vanishes. 
Furthermore,  as  will  be  seen  later,  the  three  ratios  now  give  closely 
13 


194  THE    ATOMIC    WEIGHTS. 

agreeing  values  for  the  atomic  weight  of  titanium.  The  cross  ratio, 
4AgCl  :  Ti02  is  not  directly  given  by  either  of  Thorpe's  series  ;  but  the 
data  furnished  by  Rose  and  Demoly  combine  into  a  general  mean  of 
4AgCl  :  Ti02  :  :  100  :  13.980,  ±  .0303. 

Some  two  years  later  Thorpe  published  his  work  more  in  detail,*  and 
added  a  set  of  determinations,  like  those  made  upon  the  chloride,  in 
which  titanium  tetrabromide  was  studied.  Three  ratios  were  measured, 
as  was  the  case  with  the  chloride.  In  the  first,  the  bromide  was  decom- 
posed by  water  and  titrated  with  a  silver  solution. 

TiBr±.  Ag.  TiBr±  :  rooAg. 

2.854735  3-34927  85.235 

3.120848  3.66*22  85.241 

4-73"i8  5-55°97  85.230 

6.969075  8.17645  85.234 

6.678099  7.83493  85.234 

Mean,  85.235,  +  .0027 

In  the  four  last  experiments  of  the  preceding  series,  the  silver  bromide 
formed  was  weighed.  The  third  column  gives  the  TiBr4  proportional  to 
100  parts  of  AgBr. 

TiBr^.                               AgBr,  Ratio. 

3.120848                             6.375391  48.951 

4.731118                             9-663901  48.957 

6.969075  14.227716  48.982 

6.678099  I3-639956  48.959 

Mean,  48.962,  ±  .0049 

For  the  third  ratio  the  bromide  was  decomposed  by  water  ;  and  after 
evaporation  with  ammonia  the  residual  titanic  oxide  was  ignited  and 


TiO.,.  Percent.  TiO2. 
6.969730                            1.518722  21.790 

8.836783  1.923609  21.768 

9.096309  .     I-9795J3  21.762 

Mean,  21.773,  ±  .0062 

Ignoring  Mosander's  work  as  unavailable,  we  have  the  following  ratios 
to  consider  : 

(I.)  4Ag  :  TiCl4  :  :  100  :  44.017,  i  .0031 
(2.)  4AgCl  :  TiCl4  :  :  100  :  33-I23,  ±  .0019 
(3.)  4AgCl  :  TiO2  :  :  100  :  13.980,  =h  .0303 
(4.)  TiCl4  :  TiO2  ::  100  :  42.171,  ±  .0022 
(5.)  4Ag  :  TiBr,  :  :  100  :  85.235,  ±  .0027 
(6.)  4AgBr  :  TiBr4  :  :  100  :  48.962,  ±  .0049 
(7.)  TiBr4  :  TiO2  :  :  100  :  21.773,  ±  .0062 

*  Journ.  Chem.  Soc.,  Feb.,  1885,  p.  108,  and  March,  p.  129. 


GERMANIUM.  195 

These  are  to  be  computed  with  — 

O   =  --   15.879,  +  .0003  Br     —   79.344,  zb  .0062 

Ag  =  107.  108,  ±  .0031  AgCl  =  142.287,  ±  .0037 

cl  =    35-z79,  =b  -0°48  AgBr  =  186.454,  =b  -°°54 

For  the  molecular  weight  of  titanium  chloride  they  give  two  values  : 

From  (i)  ......................  TiCl4==  188.583,  ±.0144 

From  (2)   ......................       "       =  188.519,  rb  .0119 

General  mean  .............  TiCl4  =  188.545,  ±  .0092 

For  TiBr  we  have  — 


From  (5)  ......................  TiBr4  =  365.i74,  ±  .0157 

From  (6)  ......................      "      =  365.163,^.0380 

General  mean  ............  TiBr4  =  365.  172,  =b  .0145 

And  for  the  atomic  weight  of  titanium  five  values  are  calculable,  as 
follows  : 

From  molecular  weight  of  TiCl4  ......  Ti  =  47.829,  rb  .0213 

From  molecular  weight  of  TiBr4.  .....    "  =47.796,  rb  .0260 

From  (3)  ..........................    "  =  47.809.  ±  .1725 

From  (4)  ----  ,  .....................    "  =47.698,  ±.0268 

From  (7)  .......  ..................    "  =  47-738,  ±  .0787 

General  mean  .....  .  ...........  Ti  =  47.786,  d=  .0138 

If  0  =  16,  this  becomes  Ti  =  48.150. 


GERMANIUM. 

The  data  relative  to  the  atomic  weight  of  germanium  are  rather  scanty, 
and  are  due  entirely  to  the  discoverer  of  the  element,  Winkler.*  The 
pure  tetrachloride  was  decomposed  by  sodium  carbonate,  mixed  with  a 
known  excess  of  standard  silver  solution,  and  then  titrated  back  with 
ammonium  sulphocyanate.  The  data  given  are  as  follows  : 


Cl  Found.  Percent.  Cl. 
.1067                               .076112  66.177 

.1258  .083212  66.146 

.2223  .147136  66.188 

.2904  .192190  66.182 


Mean,  66.173 

Hence,  with  Cl  =  35.179,  Ge  =  71.933.     If  O  =  16,  Ge  =  72.481. 

*  Journ.  fiir  Prakt.  Chem.  (2),  34,  177.     1886. 


196  THE   ATOMIC    WEIGHTS. 


ZIRCONIUM. 

The  atomic  weight  of  zirconium  has  been  determined  by  Berzelius, 
Hermann,  Marignac,  Weibull,  and  Bailey.  Berzelius*  ignited  the 
neutral  sulphate,  and  thus  ascertained  the  ratio  in  it  between  the  Zr02 
and  the  SO3.  Putting  S03  at  100,  he  gives  the  following  proportional 
quantities  of  Zr02 : 

75-84 

75-92 

75.80 

75-74- 

75-97 

75.85 

Mean,  75.853,  ±  .023 

This  gives  43.134,  ±  .0142  as  the  percentage  of  zirconia  in  the  sulphate. 

Hermann's  t  estimate  of  the  atomic  weight  of  zirconium  was  based 
upon  analyses  of  the  chloride,  concerning  which  he  gives  no  details  nor 
weighings.  From  sublimed  zirconium  chloride  he  finds  Zr  =  831.8, 
when  0  =  100;  and  from  two  lots  of  the  basic  chloride  2ZrOCl2,9H20, 
Zr  =  835.65  and  851.40  respectively.  The  mean  of  all  three  is  839.62  ; 
whence,  with  modern  formulae  and  O  =  15.879,  Zr  becomes  =  88.882. 

Marignac's  results  J  were  obtained  by  analyzing  the  double  fluoride  of 
zirconium  and  potassium.  His  weights  are  as  follows  : 

i.ooo  grm.  gave  .431  grm.  ZrO2  and  .613  grm.  K2SO4. 

2.000  "         .864  "  1.232  " 

.654  "         .282  "  .399 

5.000          "      2.169  3-°78  " 

These  figures  give  us  three  ratios.  A,  the  Zr02  from  100  parts  of  salt; 
B,  the  K2SO4  from  100  parts  of  salt ;  and  C,  the  ZrO2  proportional  to  100 
parts  of  K2SO, : 

A.  B.  C. 

43.100  61.300  70-310 

43.200  61.600  70.130 

43.119  61.000  70.677 

43.380  61.560  70.468 

Mean,  43.200,  d=  .043       Mean,  61.365,  =h  .094       Mean,  70.396,  ±  079. 

Weibull,§  following  Berzelius,  ignited  the  sulphate,  and  also  made  a 

*Poggend.  Annal  ,  4,  126.     1825. 

t  Journ.  fi'ir  Prakt.  Chem.,  31,  77.     Berz.  Jahresb.,  25,  147. 

jAnn.  Chim.  Phys.  (3),  60,  270.     1860. 

I  Lund.  Arsskrift,  v.  18.     i88i-'82. 


ZIRCONIUM,  197 

similar  set  of  experiments  with  the  selenate  of  zirconium,  obtaining  re- 
sults as  follows : 

Sulphate.     Zr(SO^v 

1.5499  grm.  salt  gave  .6684  ZrO2.      43.126  per  cent. 

1-5445  "  -6665  "  43-r53  " 

2.1683  "  .9360  "  43.168  " 

1.0840  "  .4670  "  43.081  " 

.7913  "  .3422  "  43-321  " 

.6251  .2695  "  43. 113  " 

.4704  .2027  "  43.09i  " 

Mean,  43.150,  =fc  .0207 

Selenate.  Zr(SeO^. 

i. 02 1 2  grm.  salt  gave  .3323  ZrO2.  32.540  per  cent. 

.8418      "     .2744  "  32.597   " 

.6035  .1964  "  32.544   " 

.8793  .2870  "  32.640   " 

.3089      "      .1003  "  32.470   " 


Mean,  32.558,  ±  .0192 

Bailey  *  also  ignited  the  sulphate,  after  careful  investigation  of  his 
material,  and  of  the  conditions  needful  to  ensure  success.  He  found  that 
the  salt  was  perfectly  stable  at  400°,  while  every  trace  of  free  sulphuric 
acid  was  expelled  at  350°.  The  chief  difficulty  in  the  process  arises  from 
the  fact  that  the  zirconia  produced  by  the  ignition  is  very  light,  and 
easily  carried  off  mechanically,  so  that  the  percentage  found  is  likely  to 
be  too  low.  This  difficulty  was  avoided  by  the  use  of  a  double  crucible, 
the  outer  one  retaining  particles  of  zirconia  which  otherwise  might  be 
lost.  The  results,  corrected  for  buoyancy  of  the  air,  are  as  follows  : 

2.02357  salt  gave    .87785  ZrOa.  43-38i  per  cent. 

2.6185  "  I.I3S4  "  43-36o  " 

2.27709  "          .98713  "  43-35°  " 

2.21645  "          -96152  "  43-385  " 

L75358  "          .76107  "  43-402  " 

1.64065  "          .7120  "  43.397  " 

2.33255  "  1.01143  "  43.36i  "  • 

1.81105  "          .78485  "  43-337  " 


Mean,  43.372,  ±  .0056 

This,  combined  with  previous  determinations,  gives — 

Berzelius 43. 134,  ±  .0142 

Weibull 43. 150,  ±  .0207 

Bailey 43-372,  ±  .0056 

General  mean 43-3I7,  ±  .0051 

*  Proc.  Roy.  Soc.,  46,  74.     Chem.  News,  60,  32. 


198  THE   ATOMIC    WEIGHTS. 

For  computing  the  atomic  weight  of  zirconium  we  now  have  the  sub- 
joined ratios : 

(i.)  Percentage  ZrO2  in  Zr(SO4)2,  43.317,  ±  .0051 

(2.)  Percentage  ZrO2  in  Zr(SeO4)2,  32.558,  ±  .0192 

(3.)  Percentage  ZrO2  from  K2ZrF6,  43.200,  ±  .043 

(4.)  Percentage  K2SO4  from  K2ZrF6,  61.365,  ±  .094 

(5.)  K2S04  :  Zr02  :  :  100  :  70.396,  ±  .079 

Tlie  antecedent  atomic  weights  are — 

O  =  15.879,  ±  .0003  K  =  38.817,  dt  .0051 

S  =31.828,  ±  .0015  F  =  18.912,  ±  .0029 

Se  =  78.419,  ±  .0042 

With  these  data  we  first  get  three  values  for  the  molecular  weight  of 
zirconia : 

From  (i) ZrO2  —  121.454,  ±  .0182 

From  (2) "  =  121.708,  ±  .0798 

From  (5) "  =  121.770,  ±  .1370 


General  mean ZrO2  —  121.471,  ±  .0176 

Finally,  there  are  three  independent  estimates  for  the  atomic  weight 
of  zirconium  : 

From  molecular  weight  ZrO2 Zr  =  89.713,  d=  .0177 

From  ratio  (3) "  =  89.437,  ±  .2390 

From  ratio  (4) "  —  90.778,  ±  .4326 

General  mean Zr  =  89.716,  ±  .0175 

If  0  =  16,  Zr  —  90.400. 

Here  the  first  value  alone  carries  appreciable  weight. 


TIN.  199 


TIN. 

The  atomic  weight  of  tin  has  been  determined  by  means  of  the  oxide, 
the  chloride,  the  bromide,  the  sulphide,  and  the  stannichlorides  of  potas- 
sium and  ammonium. 

The  composition  of  stannic  oxide  has  been  fixed  in  two  \vays  :  by 
synthesis  from  the  metal  and  by  reduction  in  hydrogen.  For  the  first 
method  we  may  consider  the  work  of  Berzelius,  Mulder  and  Vlaanderen, 
Dumas,  Van  der  Plaats,  and  Bongartz  and  Classen. 

Berzelius  *  oxidized  100  parts  of  tin  by  nitric  acid,  and  found  that 
127.2  parts  of  Sn02  were  formed. 

The  work  done  by  Mulder  and  Vlaanderen  f  was  done  in  connection 
with  a  long  investigation  into  the  composition  of  Banca  tin,  which  was 
found  to  be  almost  absolutely  pure.  For  the  atomic  weight  determina- 
tions, however,  really  pure  tin  was  taken  prepared  from  pure  tin  oxide. 
This  metal  was  oxidized  by  nitric  acid,  with  the  following  results.  100 
parts  of  tin  gave  of  SnO2 : 

127.56— Mulder. 
127.56 — Vlaanderen. 
1 27.43 — Vlaanderen. 

Mean,  127.517,  ±  .029 

Dumas  J  oxidized  pure  tin  by  nitric  acid  in  a  flask  of  glass.  The  re- 
sulting Sn02  was  strongly  ignited,  first  in  the  flask  and  afterwards  in 
platinum.  His  weighings,  reduced  to  the.  foregoing  standard,  give  for 
dioxide  from  100  parts  of  tin  the  amounts  stated  in  the  third  column  : 

12.443  grm.  Sn  gave  15.820  grm.  SnO2.  127.14 

15.976  "  20.301          "  127.07 


Mean,  127.105,  =b  .024 

In  an  investigation  later  than  that  previously  cited,  Vlaanderen  § 
found  that  when  tin  was  oxidized  in  glass  or  porcelain  vessels,  and  the 
resulting  oxide  ignited  in  them,  traces  of  nitric  acid  were  retained. 
When,  on  the  other  hand,  the  oxide  was  strongly  heated  in  platinum, 
the  latter  was  perceptibly  attacked,  so  much  so  as  to  render  the  results 
uncertain.  He  therefore,  in  order  to  fix  the  atomic  weight  of  tin,  reduced 
the  oxide  by  heating  it  in  a  porcelain  boat  in  a  stream  of  hydrogen.  Two 
experiments  gave  Sn  =  118.08,  and  Sn  =  118.24.  These,  when  0  =s  16, 
become,  if  reduced  to  the  above  common  standard, 


*Poggend.  Annal.,  8,  177. 

t  Journ.  fur  Prakt.  Chem.,  49,  35.     1849. 

t  Ann.  Chem.  Pharm.,  113,  26. 

3  Jahresbericht,  1858,  183. 


200  THE    ATOMIC    WEIGHTS. 

127.100 
127.064 

^  Mean,  127. 082,  =b  .012 

Van  der  Plaats  *  prepared  pure  stannic  oxide  from  East  Indian  tin 
(Banca),  and  upon  the  material  obtained  made  two  series  of  experiments  J 
one  by  reduction  and  one  by  oxidation.  The  results,  with  vacuum 
weights,  are  as  follows,  the  ratio  between  Sn  and  Sn02  appearing  in  the 

third  column : 

Oxidation  Series. 

9.6756  grm.  tin  gave  12.2967  SnO2.  127.091 

12.7356  16.1885     "  127.114 

23.4211  "  29.7667     "  127.093 

Reduction  Series. 

5-5OI5  grm-  Sn°2  Save  4.3280  tin.  127. 1 14 

4.9760  3-9T45    "  127.117 

3.8225  "  3.0278    "  127.086 

2.9935  "  2.3553    "  127.096 


Mean  of  both  series  as  one,  127.102,  ±  .0033 

The  reductions  were  effected  in  a  porcelain  crucible. 

Bongartz  and  Classen  f  purified  tin  by  electrolysis,  and  oxidized  the 
electrolytic  metal  by  means  of  nitric  acid.  The  oxide  found  was  dried 
over  a  water-bath,  then  heated  over  a  weak  flame,  and  finally  ignited  for 
several  hours  in  a  gas-muffle.  Some  reduction  experiments  gave  values 
which  were  too  low.  The  oxidation  series  was  as  follows,  with  the  usual 
ratio  added  by  me  in  a  third  column  : 

Sn.  SnO^  Ratio. 

2.5673  3-257o  126.865 

3.8414  4-8729  126.852 

7.3321  9.2994  126.831 

5.4367  6.8962  126.845 

7.3321  9-2994  126.831 

9.8306  12.4785  126.935 

11.2424  14.2665  126.896 

5.5719  7.0685  126.860 

9.8252  12.4713  126.932 

4-3959  5-5795  126.925 

6.3400  8.0440  126.877 

Mean,  126.877,  ±  .0080 

-  We  now  have  six  series  of  experiments  showing  the  amount  of  SnOa 
formed  from  100  parts  of  tin.  To  Berzelius'  single  determination  may  be 
assigned  the  weight  of  one  experiment  in  Mulder  and  Vlaanderen's 
series : 

*  Corapt.  Rend.,  100,  52.     1885. 

fBerichte  Deutsch.  Chem.  Gesell.,  21,  2900.     1888. 


TIN. 


201 


Berzelius 127.20x3,  ±  .041 

Mulder  and  Vlaanderen 127.517,  dr  .029 

Dumas 127. 105,  ±  .024 

Vlaanderen 127.082,  d=  .012. 

Van  der  Plaats 127. 102,  ±  .0033 

Bongartz  and  Classen 126.877,  ±  .0080 


General  mean , 127.076,  dr  .0026 

Dumas,  in  the  paper  previously  quoted,  also  gives  the  results  of  some 
experiments  with  stannic  chloride,  SnCl4.  This  was  titrated  with  a  solu- 
tion containing  a  known  weight  of  silver.  From  the  weighings  given, 
100  parts  of  silver  correspond  to  the  quantities  of  SnCl4  named  in  the 
third  column : 

1.839  grm.  SnC!4  —  3.054  grm.  Ag.  60.216 

2.665  4.427          "  60.199 

Mean,  60.207,  =t  '°°6 

Tin  tetrabromide  and  the  stannichlorides  of  potassium  and  ammonium 
were  all  studied  by  Bongartz  and  Classen ;  who,  in  each  compound, 
carefully  purified,  determined  the  tin  electrolytically.  The  data  given 
are  as  follows,  the  percentage  columns  being  added  by  myself: 


Taken. 
8.5781 

9-5850 

9.9889 
10.4914 
16.8620 
16.6752 
11.1086 
10.6356 
11.0871 
19.5167 


Tin  Tetrabromide. 
Sn  Found. 
2.3270 
2.6000 
2.7115 
2.8445 

4.5735 
4.5236 


2.8840 
3.0060 
5-2935 


Percent.  Sn. 

27.127 
27.126 

27.145 
27.113 
27.123 
27.119 
27.116 

27.113 
27.123 
27.128 


Mean,  27.123,  dr  .0020 


2.5718 
2.2464 

9-3353 

12.1525 
12.4223 
15.0870 
10.4465 
18.9377 
18.4743 
17.6432 


Potassium  Stannichloride. 

Sn  Found.  Per  cent.  Sn. 

.7472  29.054 

.6524  29.042 

2.7100  29.030 
3-5285                      ^        29.035 

3.6070  29.036 

4.3812  29.040 

3.0330  29.034 

5.5029  29.058 

5.3630  29.029 

5.1244  29.045 


Mean,  29.040,  ±  .0021 


202  THE    ATOMIC    WEIGHTS. 

Ammonium  Stannichloride. 

Am^SnQl^  Sn  Found.                    Per  cent.  Sn. 

1-6448  .5328  32.393 

1.8984  .6141  32.347 

2.0445  .6620  32.381 

2.0654  .6690  32.391 

2.0058  .6496  32.386 

2.4389  .7895  32.371 

4.0970  L3254  32. 351 

3.4202  1.1078  32.390 

3.6588  1.1836  32.349 

1.5784  .5108  32-362 

7.3248  2.3710  32.37° 

13.1460  4.2528  32.351 

11.9483  3-8650  32.348 

18.4747  5.9788  32-362 

18.6635  6.0415  32.371 

17.8894  5.7923  32.378 


Mean,  32.369,  ±  .0088 

One  other  method  of  determination  for  the  atomic  weight  of  tin  was 
employed  by  Bongartz  and  Classen.  Electrolytic  tin  was  converted  into 
sulphide,  and  the  sulphur  so  taken  up  was  oxidized  by  means  of  hydrogen 
peroxide,  by  Classen's  method,  and  weighed  as  barium  sulphate.  The 
results,  as  given  by  the  authors,  are  subjoined : 

Sn  Taken.  Per  cent,  of  S  Gained. 

2.6285  53.91 

•  7495  53.87 

1.4785  53-94 

2.5690  53.94 

2.1765  53.85 

1.3245  53-88 

•9897  53.83 

2.7160  53-86 


Mean,  53.885,  =h  .0098 

This  percentage  of  sulphur,  however,  was  computed  from  weighings 
of  barium  sulphate.  What  values  were  assigned  to  the  atomic  weights 
of  barium  and  sulphur  is  not  stated,  but  as  Meyer  and  Seubert's  figures 
are  used  for  other  elements  throughout  this  paper,  we  may  assume  that 
they  apply  here  also.  .  Putting  O  =  15.96,  S  =  31.98,  and  Ba  =  136.86, 
the  53.885  per  cent,  of  sulphur  becomes  392.056,  ±  .0713  of  BaS04,  the 
compound  actually  weighed.  This  gives  us  the  ratio — 

Sn  :  2BaSO4  :  :  loo  :  392.056,  d=  .0713 

as  the  real  result  of  the  experiments,  from  which,  with  the  later  values 
for  Ba,  S,  and  0,  the  atomic  weight  of  tin  may  be  calculated. 


TIN.  203 

We  now  have,  for  tin,  the  following  available  ratios : 

(l.)   Sn  :  SnO2  :  :  loo  :  127.076,  dr  .0026 

(2.)  4Ag  :  SnG4  :  :  100  :  60.207,  ±  -0060 

(3.)  Percentage  of  tin  in  SnBr4>  27.123,  ±  .0020 

(4.)   Percentage  of  tin  in  K2SnCl6,  29.040,  ±  .0021. 

(5.)  Percentage  of  tin  in  Am2SnCI6,  32.369,  ±  .0088 

(6.)  Sn  :  2BaSO4  :  :  100  :  392.056,  ±  .0713 

The  antecedent  values  are — 

O   =   15.879,  ±  .0003  K=  38.817,  d=  .0051 

Ag  =  107.108,  rb  .0031  N    =     13.935,  ±  .0021 

Cl  =    35.179,  ±  .0048  S    =    31.828,  ±.0015 

Br  =    79.344,  dr  .0062  Ba  =  136.392,  ±  .0086 

With  these,  six  independent  values  for  Sn  are  computable,  as  follows  : 

From  (i). Sn  —  117.292,  ±  .0115 

From  (2) "  =  117.230,  =h  -0331 

From  (3) "  =  1 18.120,  ±  .0131 

From  (4) "  =  118.152,  d=. 0155 

From  (5) "  =  118.190,  ±  .0382 

From  (6) "  =  118.216,  ±  .0220 

General  mean Sn  =  1 17.805,  ±  .0069 

If  0  =  16,  Sn  =  118.701. 

If  we  reject  the  first  two  of  these  values,  which  include  all  of  the  older 
work,  and  take  only  the  last  four,  which  represent  the  concordant  results 
of  Bongartz  and  Classen,  the  general  mean  becomes — 

Sn  —  1 1 8. 150,  =b  .0089 

Or,  with  O  =  16,  Sn  =  119.050.  This  mean  I  regard  as  having  higher 
probability  than  the  other. 

A  single  determination  of  the  atomic  weight  of  tin,  made  by  Schmidt,* 
ought  not  to  be  overlooked,  although  it  was  only  incidental  to  his  research 
upon  tin  sulphide.  In  one  experiment,  0.5243  grm.  Sn  gave  0.6659  Sn02. 
Hence,  with  0  =  16,  Sn  =  118.49.  This  lies  about  midway  between  the 
two  sets  of  values  already  computed. 

*  Berichte,  27,  2743.     1894. 


204  THE   ATOMIC   WEIGHTS. 


THORIUM. 

The  atomic  weight  of  thorium  has  been  determined  from  analyses  of 
the  sulphate,  oxalate,  formate,  and  acetate,  with  widely  varying  results. 
The  earliest  figures  are  due  to  Berzelius,*  who  worked  with  the  sulphate, 
and  with  the  double  sulphate  of  potassium  and  thorium.  The  thoria 
was  precipitated  by  ammonia,  and  the  sulphuric  acid  was  estimated  as 
BaS04.  The  sulphate  gave  the  following  ratios  in  two  experiments.  The 
third  column  represents  the  weight  of  ThO2  proportional  to  100  parts  of 
BaSO, : 

•6754  grm-  ThO2  —  1.159  grm.  BaSO4.         Ratio,  58.274 
1.0515  "  1.832  «  "       57.396 

The  double  potassium  sulphate  gave  .265  grm.  Th02,  .156  grin.  S03, 
and  .3435  K2S04.  The  S03,  with  the  Berzelian  atomic  weights,  repre- 
sents .4537  grm.  BaS04.  Hence  100  BaSO4  is  equivalent  to  58.408  Th02. 
This  figure,  combined  with  the  two  previous  values  for  the  same  ratio, 
gives  a  mean  of  58.026,  ±  .214. 

From  the  ratio  between  the  K2S04  and  the  Th02  in  the  double  sul- 
phate, Th02  =  266.895. 

In  1861  new  determinations  were  published  by  Chydenius.t  whose 
memoir  is  accessible  to  me  only  in  an  abstract  J  which  gives  results  with- 
out details.  Thoria  is  regarded  as  a  monoxide,  ThO,  and  the  old  equiv- 
alents (O  =  8)  are  used.  The  following  values  are  assigned  for  the 
molecular  weight  of  ThO,  as  found  from  analyses  of  several  salts  : 

From  Sulphate.      From  K.  Th.  Sulphate. 
66.33  67.  °2 

67.13 

67.75 
68.03 


Mean,  67.252,  d=  .201 

From  Acetate.  From  Formate.  From  Oxalate. 

67.31  68.06  65.87-^  Two  results 

66.59  67.89  65.95  j     by  Berlin. 

67.27  68.94  65.75 

67.06  65.13 

68.40  Mean,  68.297,  rb  .219  6654 

65.85 

Mean,  67.326,  ±  .201 

Mean,  65.85,  ±  .123 

*  Poggend.  Annal.,  16,  398.     1829.     Lehrbuch,  3,  1224. 

t  Keraisk  undersokning  af  Thorjord  och  Thorsalter.     Helsingfors,  1861.     An  academic  disser- 
tation. 
I  Poggeud.  Annal.,  119,  55.     1863. 


THORIUM. 


205 


We  may  fairly  assume  that  these  figures  were  calculated  with  0  =  8, 
C  =  6,  and  S  •=  16.  Correcting  by  the  values  for  these  elements  which 
have  been  found  in  previous  chapters,  Th02  becomes  as  follows : 

From  sulphate ThO2  =  267.170,  rfc  .7950 

From  acetate "     =  267.488,  ±  .7950 

From  formate "     =  271.239,  ±  .8698 

From  oxalate "     =  261.478,  d=  .4884 


General  mean  .............  ThO2  =  265.103,  ±  -3394 

The  single  result  from  the  double  potassium  sulphate  is  included  with 
the  column  from  the  ordinary  sulphate,  and  the  influence  of  the  atomic 
weight  of  potassium  is  ignored. 

Chydenius  was  soon  followed  by  Marc  Delafontaine,  whose  researches 
appeared  in  1863.*  This  chemist  especially  studied  thorium  sulphate  ; 
partly  in  its  most  hydrous  form,  partly  as  thrown  down  by  boiling.  In 
Th(S04)2.9H20,  the  following  percentages  of  Th02  were  found  : 

45.08 
44.90 
45.06 

45-21 
45.06 

Mean,  45.062,  dz  .0332 

The  lower  hydrate,  2Th(SO4)2.9H20,  was  more  thoroughly  investi- 
gated. The  thoria  was  estimated  in  two  ways  :  First  (A),  by  precipita- 
tion as  oxalate  and  subsequent  ignition  ;  second  (B),  by  direct  calcination. 
These  percentages  of  Th02  were  found  : 

52.83! 


52.72 

52.I3J 

52.47 

52.49 

52.53 

52-13 

52.13 

52.43 

52.60 

52.40 

52.96 

52.82 


Mean,  52.511,  ±  .047 

In  three  experiments  with  this  lower  hydrate  the  sulphuric  acid  was 
also  estimated,  being  thrown  down  as  barium  sulphate  after  removal  of 
the  thoria : 


*Arch.  Sci.  Phys.  et  Nat.  (2),  18,  343. 


206  THE    ATOMIC    WEIGHTS. 

1.2425  grm.  gave  .400  SO3.  (1.1656  grm.  BaSO4.) 

1.138  "  .366    "  (1.0665  "  ) 

.734  «          .2306  «  (  .6720  «  ) 

The  figures  in  parentheses  are  reproduced  by  myself  from  Delafon- 
taine's  results,  he  having  calculated  his  analyses  with  O  =  100,  S  =  200, 
and  Ba  =  857.  These  data  may  be  reduced  to  a  common  standard,  so 
as  to  represent  the  quantity  of  2Th(S04)2.9H20,  equivalent  to  100  parts 
of  BaS04.  We  then  have  the  following  results  : 

106.597 
106.704 
109.226 


Mean,  107.509,  ±  .585 


Delafontaine  was  soon  followed  by  Hermann,*  who  published  a  single 
analysis  of  the  lower  hydrated  sulphate,  as  follows : 

Th02 52.87 

S03 32.11 

H20 15.02 


IOO.OO 

Hence,  from  the  ratio  between  S03  and  Th02,  Th02  =  262.286.  Prob- 
ably the  S03  percentage  was  loss  upon  calcination. 

Both  Hermann's  results  and  those  of  Delafontaine  are  affected  by  one 
serious  doubt,  namely,  as  to  the  true  composition  of  the  lower  hydrated 
sulphate.  The  latest  and  best  evidence  seems  to  establish  the  fact  that 
it  contains  four  molecules  of  water  instead  of  four  and  a  half,f  a  fact 
which  tends  to  lower  the  resulting  atomic  weight  of  thorium  consid- 
erably. In  the  final  discussion  of  these  data,  therefore,  the  formula 
Th(S04)2.4H20  will  be  adopted.  As  for  Hermann's  single  analysis,  his 
percentage  of  Th02,  52.87,  may  be  included  in  one  series  with  Delafon- 
taine's,  giving  a  mean  of  52.535,  ±  .0473. 

The  next  determinations  to  consider  are  those  of  Cleve,J  whose  results, 
obtained  from  both  the  sulphate  and  the  oxalate  of  thorium,  agree  ad- 
mirably. The  anhydrous  sulphate,  calcined,  gave  the  subjoined  per- 
centages of  thoria : 

62.442 

62.477 

62.430 

62.470 

62.357 
•  62.366 

Mean,  62.423,  ±  .014 

*  Journ.  fur  Prakt.  Chetn.,  93,  114. 

t  See  Hillebrand,  Bull.  90,  U.  S.  Geol.  Survey,  p.  29. 

I  K.  Sveuska  Vet.  Akad.  Handling.,  Bd.  2,  No.  6,  1874. 


THORIUM.  207 

The  oxalate  was  subjected  to  a  combustion  analysis,  whereby  both 
thoria  and  carbonic  acid  could  be  estimated.  From  the  direct  percentages 
of  these  constituents  no  accurate  value  can  be  deduced,  there  having 
undoubtedly  been  moisture  in  the  material  studied.  From  the  ratio 
between  C02  and  Th02,  however,  good  results  are  attainable.  This  ratio 
I  put  in  a  fourth  column,  making  the  thoria  proportional  to  100  parts  of 
carbon  dioxide : 

Oxalate.  ThO^.  CO.,.  Ratio. 

I-7I35  Srm-  1.0189  grm.  .6736  grm.  151.262' 

1.3800     "  .8210     "  .5433     "  151.114 

1.1850     "  .7030     "  -4650     "  151.183 

1.0755     "  .6398     "  .4240     "  150.896 


Mean,  151.114,  ±  .053 

Iii  1882,  Nilson's  determinations  appeared.*  This  chemist  studied 
both  the  anhydrous  sulphate,  and  the  salt  with  nine  molecules  of  water, 
using  the  usual  calcination  method,  but  guarding  especially  against  the 
hygroscopic  character  of  the  dry  Th  (SOJ2  and  the  calcined  Th02.  The 
hydrated  sulphate  gave  results  as  follows : 


Percent.  ThO.,. 


2.0549  .9267  45.097 

2.1323  .9615  45-092 

3.0017  1.3532  45-081 

2.7137  1.2235  45-086 

2.6280  1.1849  45.088 

1.9479  .8785  45..  099 

Mean,  45.091,  ±  .0019 
Delafontaine  found,  45.062,  it  .0332 


General  mean,  45.090,  ±  .0019 

The  anhydrous  sulphate  gave  data  as  follows : 

Th(SO^.  ThOv  Percent. 

1.4467  -9013  62.300 

1.6970  1.0572  62.298 

2.0896  1.3017  62.294 

1.5710  .9787  62.298 


Mean,  62.297,  =b  .0009 

The  last  four  determinations  appear  again  in  a  paper  published  five 
years  later  by  Kriiss  and  Nilson,f  who,  however,  give  four  more  made 


*Ber.  Deutsch.  Chem.  Gesell.,  15,  2519.     1882. 
f  Ber.  Deutsch.  Chem.  Gesell.,  20,  1665.    1887. 


208  THE  'ATOMIC    WEIGHTS. 

upon  material  obtained  from  a  different  source.     The  new  data  are  sub- 
joined : 

Th(SOJv  ThO2.  Percent.  ThO.,. 

1.1630  .7245                                62.296 

.8607  .5362                                62.298- 

1.5417  .9605                                62.301 

1.5217  .9479  •       62.292 

Mean,  62.297,  ±  .0013 

Nilson's  series,  62.297,  ±  .0009 

Cleve  found,  62.423,  zb  .0140 


General  mean,  62.298,  ±  .0007 

From  Chydenius'  work  we  have  four  values  for  the  molecular  weight 
of  thoria,  which,  combined  as  usual,  give  a  general  mean  of  Th02  = 
265.103,  db  .3394.     We  also  have  the  following  ratios  : 

(I.)   2BaSO4  :  ThO2  :  :  ZOO  :  58.026,  dz  .214 

(2.)  2BaSO4  :  Th(SO4)2.4H2O  :  :  100  :  107.509,  ±  .585 

(3.)  4CO2  :  ThO2  ::  100  :  151.114,  ±  .053 

(4.)   Percentage  of  ThO2  in  Th(SO4)2.9H2O,  45.090,  =b  .0019 

(5.)  Percentage  of  ThO2  in  Th(SO4)2.4H2O,  52.535,  ±  .0473 

(6.)    Percentage  of  ThO2  in  Th(SO4)2.62.298,  =h  .0007 

Reducing  with  the  following  data,  seven  values  for  the  atomic  weight 
of  thoria  are  calculable  : 

O  =  15.879,  ±  .0003  C  =   11.920,  ±  .0004 

S  =  31.828,  ±  .0015  Ba  =  136.392,  ±  .0086 

The  values  for  Th02  are— 

Chydenius'  determinations ThO2  —  265.103,  ±  -3394 

From(i) «  =268.937,  ±  -9919 

From  (2) "  rr=  268.021,  ±  2.7115 

From  (3) "  =264. 1 20,  dr  .0927 

From  (4) "  =262.641,  ±  .0149 

From  (5) "  =  255.061,  ±  .3426 

From  (6) "  =262.613,  ±  .0081 

General  mean ThO2  =  262.626,  ±    .0071 

Hence  Th  =  230.868,  ±  .0071. 
If  0  =  16,  Th  =  232.626. 


PHOSPHORUS.  209 


PHOSPHORUS. 

The  material  from  which  we  are  to  calculate  the  atomic  weight  of 
phosphorus  is  by  no  means  abundant.  Berzelius,  in  his  Lehrbuch,* 
adduces  only  his  own  experiments  upon  the  precipitation  of  gold  by 
phosphorus,  and  ignores  all  the  earlier  work  relating  to  the  composition 
of  the  phosphates.  These  experiments  have  been  considered  with  refer- 
ence to  gold. 

Pelouze,t  in  a  single  titration  of  phosphorus  trichloride  with  a  stand- 
ard solution  of  silver,  obtained  a  wholly  erroneous  result ;  and  Jacque- 
lain,  J  in  his  similar  experiments,  did  even  worse.  Schrdtter's  criticism 
upon  Jacquelain  sufficiently  disposes  of  the  latter.  § 

Only  the  determinations  made  by  Schrotter,  Dumas,  and  Van  der 
Plaats  remain  to  be  considered. 

Schrotter  ||  burned  pure  amorphous  phosphorus  in  dry  oxygen,  and 
weighed  the  pentoxide  thus  formed.  One  gramme  of  P  yielded  P203  in 

the  following  proportions : 

2.28909 
2.28783 
2.29300 
2.28831 
2.29040 
2.28788 
2.28848 
2.28856 
2.28959 
2.28872 

Mean,  2.289186,  =h  .60033 

Dumas  ^|  prepared  pure  phosphorus  trichloride  by  the  action  of  dry 
chlorine  upon  red  phosphorus.  The  portion  used  in  his  experiments 
boiled  between  76°  and  78°.  This  was  titrated  with  a  standard  solution 
of  silver  in  the  usual  manner.  Dumas  publishes  weights,  from  which  I 
calculate  the  figures  given  in  the  third  column,  representing  the  quantity 
of  trichloride  proportional  to  100  parts  of  silver  : 

1.787  grm.  PC13  =  4.208  grm.  Ag.  42.4667 

1.466  "  3.454       "  42.4435 

2.056  "  4.844       "  42.4443 

2.925  "  6.890       "  42.4528 

3.220  7.582        "  42.4690 

Mean,  42.4553,  d=  .0036 

*5th  ed.,  1188. 
fCompt.  Rend.,  20,  1047. 
J  Compt.  Rend.,  33,  693. 
%  Journ.  fur  Prakt.  Cheni.,  57,  315. 
||  Journ.  fur  Prakt.  Chera.,  53,  435.     1851. 
11  Ann.  Chem.  Pharm.,  113,  29.     1860. 
14 


210  THE    ATOMIC    WEIGHTS. 

By  Van  der  Plaats*  three  methods  of  determination  were  adopted, 
and  all  weights  were  reduced  to  vacuum  standards.  First,  silver  was 
precipitated  from  a  solution  of  the  sulphate  by  means  of  phosphorus. 
The  latter  had  been  twice  distilled  in  a  current  of  nitrogen.  The  silver, 
before  weighing,  was  heated  to  redness.  The  phosphorus  equivalent  to 
100  parts  of  silver  is  given  in  the  third  column. 

.9096  grm.  P  gave  15.8865  Ag.  5-7256 

.5832  "  10.1622    "  5.7389 

Mean,  5.7322,  ±  .0045 

The  second  method  consisted  in  the  analysis  of  silver  phosphate  ;  but 
the  process  is  not  given.  Van  der  Plaats  states  that  it  is  difficult  to  be 
sure  of  the  purity  of  this  salt. 

6.6300  grm.  Ag3PO4  gave  5.1250  Ag.  77.3°°  Per  cent. 

12.7170  "  9.8335    "  77.326       " 


Mean,  77.313,  ±  .0088 

In  the  third  set  of  determinations,  yellow  phosphorus  was  oxidized  by 
oxygen  at  reduced  pressure,  and  the  resulting  P205  was  weighed. 

10.8230  grm.  P  gave  24.7925  P2O5.  Ratio,  2  29072 

7.7624  «  I7-79J5     "  "       2.29201 

As  these  figures  fall  within  the  range  of  Schrotter's,  they  maybe  aver- 
aged in  with  his  series,  the  entire  set  of  twelve  determinations  giving 
a  mean  of  2.28955,  ±  .00032. 

From  the  following  ratios  an  equal  number  of  values  for  P  may  now 
be  computed : 

(i.)  2P  :  P2O3  :  :  l.o  :  2.28955,  ±  .00032 
(2.)  3Ag  :  PC13  :  :  100  :  42-4553,  ±  -0036 
(30   5AS  :  p  :  :  I0°  :  5-7322,  ±  .0045 
(4.)  Ag3PO4  :  3Ag  :  :  100  :  77.313,  ±  .0088 

Starting  with  0  =  15.879,  ±  .0003,  Ag  =  107.108,  ±  .0031,  and  Cl  = 
35.179,  ±  .0048,  we  have— 

From  (i) P  =  30.784,  =fc  .0077 

From  (2) • "  =  30.882,  ±  .0189 

From  (3) "  —  30.698,  =b  .0241 

From  (4) "  =  30.774,  ±  .0382 


General  mean P  =  30.789,  ±  .0067 

If  0  =  16,  P  =  31.024. 

The  highest  of  these  figures  is  that  from  ratio  number  two,  represent- 
ing the  work  of  Dumas.  This  is  possibly  due  to  the  presence  of  oxy- 
chloride,  in  traces,  in  the  trichloride  taken.  Such  an  impurity,  if  present, 
would  tend  to  raise  the  apparent  atomic  weight  of  phosphorus. 

*Compt.  Rend.,  100,  52.     1885. 


VANADIUM.  211 


VANADIUM. 

Roscoe's  determination  of  the  atomic  weight  of  vanadium  was  the  first 
to  have  any  scientific  value.  The  results  obtained  by  Berzelius  *  and  by 
Czudnowicz  f  were  unquestionably  too  high,  the  error  being  probably 
due  to  the  presence  of  phosphoric  acid  in  the  vanadic  acid  employed. 
This  particular  impurity,  as  Roscoe  has  shown,  prevents  the  complete 
reduction  of  V2O5  to  V2O3  by  means  of  hydrogen.  All  vanadium  ores 
contain  small  quantities  of  phosphorus,  which  can  only  be  detected  with 
ammonium  molybdate  —  a  reaction  unknown  in  Berzelius'  time.  Fur- 
thermore, the  complete  purification  of  vanadic  acid  from  all  traces  of 
phosphoric  acid  is  a  matter  of  great  difficulty,  and  probably  never  was 
accomplished  until  Roscoe  undertook  his  researches. 

In  his  determination  of  the  atomic  weight,  Roscoe  J  studied  two  com- 
pounds of  vanadium,  namely,  the  pentoxide,  V2O5,  and  the  oxychloride, 
VOC13.  The  pentoxide,  absolutely  pure,  was  reduced  to  V2O3  by  heating 
in  hydrogen,  with  the  following  results  : 

7-7397  grm-  V2O5  gave  6.3827  grm.  V2O3.  17-533  Per  cent,  of  loss. 

6.5819  5-4296         "  i7-5°7 

5-1895  4-2819         "  17.489 

5.0450  4.1614         "  17.515 

5.  4296  grm.  V2O3,  reoxidized,  gave  6.  5814  grm.  V2O5.  17.501  per  cent,  difference. 

Mean,  17.509,  =b  .005 

Hence  V  =  50.993,  ±  .0219. 

Upon  the  oxychloride,  VOC13,  two  series  of  experiments  were  made  — 
one  volumetric,  the  other  gravimetric.  In  the  volumetric  series  the  com- 
pound was  titrated  with  solutions  containing  known  weights  of  silver, 
which  had  been  purified  according  to  the  methods  recommended  by 
Stas.  Roscoe  publishes  his  weighings,  and  gives  percentages  deduced 
from  them  ;  his  figures,  reduced  to  a  common  standard,  make  the  quan- 
tities of  VOCL  given  in  the  third  column  proportional  to  100  parts  of 
silver.  He  was  assisted  by  two  analysts  : 


Analyst  A. 

2.4322  grm. 

VOC13 

=  4.5525  grm.  Ag. 

53.425 

4.6840 

" 

8.7505 

53.528 

4.2188 

1  1 

7.8807         " 

53-533 

3-949° 

" 

7-3799 

53-5'Q 

•9243 

<  < 

1.7267 

53-530 

1-4330 

" 

2.6769 

53.532 

*  Poggend.  Annal.,  22,  14.     1831. 

t  Poggend.  Annal.,  120,  17.     1863. 

t  Journ.  Chem.  Soc.,  6,  pp.  330  and  344.     1868. 


212  THE   ATOMIC    WEIGHTS. 

Analyst  B. 

2.853ogrm.  VOCI3  =  5.2853  grm.  Ag.  53-98o 

2.1252            "             3-9535         "  53-755 

1.4248            "              2.6642         "  53-479 


Mean,  53.586,  =b  .039 

The  gravimetric  series,  of  course,  fixes  the  ratio  between  VOC13  and 
AgCl.  If  we  put  the  latter  at  100  parts,  the  proportion  of  VOC13  is  as 
given  in  the  third  column  : 

Analyst  A. 

1.8521  grm.  VOC13  gave  4.5932  grm.  AgCl.  40.323 

.7013  "  1.7303  "  40.531 

.7486  1.8467  "  40.537 

1.4408  3-57I9  "  40.337 

•  9453  2.3399  "  40.399 

1.6183  "  4.0282          "  40.174 

Analyst  B. 

2.1936  grm.  VOC13  gave  5.4039  grm.  AgCl.  40.391 

2.5054  "  6.2118         "  40.333 


Mean,  40.378,  ±b  .028 

These  two  series  give  us  two  values  for  the  molecular  weight  of  VOC13 : 

From  volumetric  series . .   VOC13  =  172.185,  rb  .1254 

From  gravimetric  series "      =  172.358,  ±  .1196 


General  mean VOC13  —  172.277,  zfc  .0866 

Hence  V  =  50.881,  ±  .0877. 

Combining  the  two  values  for  V,  we  have  : 

From  VOC13 V  =  50.881,  ±  .0877 

From  V2O5 "  =  50.993,  ±  .0219 


General  mean V  =  50.986,  ±  .0212 

If  0  =  16,  V  =  51.376.    These  values  are  calculated  with  0  =  15.879, 
±  .0003;    Cl  =  35.179,  ±  .0048;  Ag  =  107.108,  ±  .0031,  and   AgCl  = 

142.287,  ±  .0037. 


ARSENIC.  213 


ARSENIC. 

For  the  determination  of  the  atomic  weight  of  arsenic  three  compounds 
have  been  studied— the  chloride,  the  trioxide,  and  sodium  pyroarsenate. 
The  bromide  may  also  be  considered,  since  it  was  analyzed  by  Wallace 
in  order  to  establish  the  atomic  weight  of  bromine.  His  series,  in  the 
light  of  more  recent  knowledge,  may  properly  be  inverted,  and  applied 
to  the  determination  of  arsenic. 

In  1826  Berzelius  *  heated  arsenic  trioxide  with  sulphur  in  such  a  way 
that  only  S02  could  escape.  2.203  grammes  of  As203,  thus  treated,  gave 
a  loss  of  1.069  of  S02.  Hence  As  =  74.460. 

In  1845  Pelouzef  applied  his  method  of  titration  with  known  quan- 
tities of  pure  silver  to  the  analysis  of  the  trichloride  of  arsenic,  AsCl3. 
Using  the  old  Berzelian  atomic  weights,  and  putting  Ag  =  1349.01  and 
Cl  =  443.2,  he  found  in  three  experiments  for  As  the  values  937.9,  937.1, 
and  937.4.  Hence  100  parts  of  silver  balance  the  following  quantities 

of  AsCls: 

56.029 

56.009 
56.016 

Mean,  56.018,  ±  .004 

Later,  the  same  method  was  employed  by  Dumas, J  whose  weighings, 
reduced  to  the  foregoing  standard,  give  the  following  results : 

4.298  grm.  AsCl3  =  7.673  grm.  Ag.  Ratio,  56.015 

5.535              "             9.880         "  "       56.022 

7.660             "           13.686         "  "      55-97° 

4-680             "            8.358         "  "      55-993 

Mean,  56.000,  -_h  .008 

The  two  series  of  Pelouze  and  Dumas,  combined,  give  a  general  mean 
-of  56.014,  ±  .0035,  as  the  amount  of  AsCl3  equivalent  to  100  parts  of 
silver.  Hence  As  =  74.450,  ±  .019,  a  value  closely  agreeing  with  that 
deduced  from  the  single  experiment  of  Berzelius. 

The  same  process  of  titration  with  silver  was  applied  by  Wallace  §  to 
the  analysis  of  arsenic  tribromide,  AsBr3.  This  compound  was  repeatedly 
distilled  to  ensure  purity,  and  was  well  crystallized.  His  weighings 
.show  that  the  quantities  of  bromide  given  in  the  third  column  are  pro- 
portional to  100  parts  of  silver : 

8.3246  grm.  AsBr3=  8.58  grm.  Ag.  97.023 

4.4368  "  4-573        "  97.022 

5.098  "  5.257        "  96.970 

Mean,  97.005,  ±  .012 

*  Poggend.  Annalen,  8,  i. 
fCompt.  Rend.,  20,  1047. 
I  Ann.  Chim.  Phys.  (3),  55,  174.     1859. 
I  Phil.  Mag.  (4),  18,  270. 


214  THE    ATOMIC    WEIGHTS. 

Hence  As  =  73.668,  ±  .0436.  Why  this  value  should  be  so  much 
lower  than  that  from  the  chloride  is  unexplained. 

The  volumetric  work  done  by  Kessler.*  for  the  purpose  of  establishing 
the  atomic  weights  of  chromium  and  of  arsenic,  is  described  in  the 
chromium  chapter.  In  that  investigation  the  amount  of  potassium 
dichromate  required  to  oxidize  100  parts  of  As.2O3  to  As205  was  determined 
and  compared  with  the  quantity  of  potassium  chlorate  necessary  to  pro- 
duce the  same  effect.  From  the  molecular  weight  of  KC103,  that  of 
K2Cr2O7  was  then  calculable. 

From  the  same  figures,  the  molecular  weights  of  KC103  and  of  K2Cr20 
being  both  known,  that  of  As203  may  be  easily  determined.  The  quan- 
tities of  the  other  compounds  proportional  to  100  parts  of  As203  are  as- 

follows  : 

A-202<97.  KCIO* 

98.95  4i.i56 

98.94  41.116 

99.17  41.200 

98.98  41-255 

99.08  41.201 

99.15  41.086 

41.199 

Mean,  99.045,  ±  .028  41.224 

41.161 

4M93 
41.149 
41.126 


Mean,  41.172,  db  .009 

Another  series  with  the  dichromate  gave  the  following  figures : 

99.08 
99.06 
99.10 
98.97 
98.97 


Mean,  99.036,  ±  .019 
Previous  series,  99.045,  =b  .028 


General  mean,  99.039,  =h  .016 

Other  defective  series  are  given  to  illustrate  the  partial  oxidation  of 
the  As203  by  the  action  of  the  air.  From  Kessler's  data  we  get  two 
values  for  the  molecular  weight  of  As2O3,  thus  : 

From  KC1O3  series As2O3  =  196.951,  ±  .0445 

From  K2Cr2O7  series "      =  196.726,  db  .0562 

General  mean As2O3  =  196.851,  =b  .0349 

And  As  =  74.607,  ±  .0175. 

*  Poggend  Annal.,  95,  204.     1855.     Also  113,  134.     1861. 


ARSENIC.  215 

The  determinations  made  by  Hibbs*  are  based  upon  an  altogether 
different  process  from  any  of  the  preceding  measurements.  Sodium 
pyroarsenate  was  heated  in  gaseous  hydrochloric  acid,  yielding  sodium 
chloride.  The  latter  was  perfectly  white,  completely  soluble  in  water, 
unfused,  and  absolutely  free  from  arsenic.  The  vacuum  weights  are 
subjoined,  with  a  column  giving  the  percentage  of  chloride  obtained 
from  the  pyroarsenate. 

Na^As^O^.  NaCl.  Percentage. 

.02177  -OI439  66. 100 

.04713  .03"5     '  66.094 

.05795  .03830  66.091 

.40801  .26981  66.128 

.50466  -33345  66.092 

.77538  .51249  66.095 

.82897  .54791  66.095 

1.19124  .78731  66.092 

1.67545  1.10732  66.091 

3.22637  2.13267  66. 101 

Mean,  66.098,  ±  .0030 

Hence  As  =  74.340,  ±  .0235. 

In  the  calculation  of  the  foregoing  values  for  arsenic,  the  subjoined 
atomic  weights  have  been  assumed  : 

O   ----   15.879,  ±.0003  K  =  38.817,  ±  .0051 

Ag—  107.108,  db  .0031  Na  =  22.881,  ±  .0046 

Cl  =.  35.179,  zb  .0048  S  =  31.828,  ib. ooi  5 

Br  =  79.344,  ±  -0062  Cr  =  51.742,  ±  .0034 

To  the  single  determination  by  Berzelius  we  may  arbitrarily  assign  a 
weight  equal  to  that  of  the  result  from  Wallace's  bromide  series.  The 
general  combination  is  then  as  follows : 

From  Berzelius'  experiment As  =  74.460,  ±  .0436 

"  =  74.45°>  ±  .OI9° 

"  =  73.668,  ±  .0436 

From  As2O3  (Kessler) "  =  74.607,  ±  .0175 

From  Na4As2O7 "  =  74.340,  db  .0235 

General  mean As  —  74.440,  ±  .0106 

If  O  =  16,  As  =  75.007. 

*  Doctoral  thesis,  University  of  Pennsylvania,  1896.  Work  done  under  the  direction  of  Professor 
E.  F.  Smith.  In  the  fifth  experiment  the  weight  of  NaCl  is  printed  .33045.  This  is  evidently  a 
misprint,  which  I  have  corrected  by  comparison  with  the  other  data.  The  rejection  of  this  ex- 
periment would  not  affect  the  final  result  appreciably. 


216  THE    ATOMIC    WEIGHTS. 


ANTIMONY. 

After  some  earlier,  unsatisfactory  determinations,  Berzelius,*  in  1826, 
published  his  final  estimation  of  the  atomic  weight  of  antimony.  He 
oxidized  the  metal  by  means  of  nitric  acid,  and  found  that  100  parts  of 
antimony  gave  124.8  of  Sb2O4.  Hence,  if  O  —  16,  Sb  =  129.03.  The 
value  129  remained  in  general  acceptance  until  1855,  when  Kessler,  f  by 
special  volumetric  methods,  showed  that  it  was  certainly  much  too  high. 
Kessler's  results  will  be  considered  more  fully  further  along,  in  connec- 
tion with  a  later  paper;  for  present  purposes  a  brief  statement  of  his 
earlierj  conclusions  will  suffice.  Antimony  and  various  compounds  of 
antimony  were  oxidized  partly  by  potassium  dichromate  and  partly  by 
potassium  chlorate,  and  from  the  amounts  of  oxidizing  agent  required 
the  atomic  weight  in  question  was  deduced  : 

By  oxidation  of  Sb2O3  from  100  parts  of  Sb Sb  =  123.84 

By  oxidation  of  Sb  with  K2Cr2O7 "  —  123.61 

By  oxidation  of  Sb  with  KC1O3  +  K2Cr2O7 "  =  123.72 

By  oxidation  of  Sb2O3  with  KC1O3  +  K2Cr2O7. .  .  "  =  123.80 

By  oxidation  of  Sb2Ss  with  K2Cr2O7 "   =  123.58 

By  oxidation  of  tartar  emetic "  =  1 19.80 

The  figures  given  are  those  calculated  by  Kessler  himself.  A  recalcu- 
lation with  our  newer  atomic  weights  for  O,  K,  Cl,  Cr,  S,  and  C  would 
yield  lower  values.  It  will  be  seen  that  five  of  the  estimates  agree  closely, 
while  one  diverges  widely  from  the  others.  It  will  be  shown  hereafter 
that  the  concordant  values  are  all  vitiated  by  constant  errors,  and  that 
the  exceptional  figure  is  after  all  the  best. 

Shortly  after  the  appearance  of  Kessler's  first  paper,  Schneider  J  pub- 
lished some  results  obtained  by  the  reduction  of  antimony  sulphide  in 
hydrogen.  The  material  chosen  was  a  very  pure  stibnite  from  Arnsberg, 
of  which  the  gangue  was  only  quartz.  This  was  corrected  for,  and  cor- 
rections were  also  applied  for  traces  of  undecom posed  sulphide  carried 
off  mechanically  by  the  gas  stream,  and  for  traces  of  sulphur  retained 
by  the  reduced  antimony.  The  latter  sulphur  was  estimated  as  barium 
sulphate.  From  3.2  to  10.6  grammes  of  material  were  taken  in  each  ex- 
periment. The  final  corrected  percentages  of  S  in  Sb2S3  were  as  follows  : 

28.559 
28.557 
28.501 

28.554 
28.532 

*Poggend.  Aimalen,  8,  i. 

tPoggend.  Annalen,  95,  215. 

I  Poggend.  Annalen,  98,  293.     1856.     Preliminary  note  in  Bd.  97. 


ANTIMONY.  217 

28.485 
28.492 
28.481 


Mean,  28.520,  db  .008 

Hence,  if  S  =  32,  Sb  =  120.3. 

Immediately  after  the  appearance  of  Schneider's  memoir,  Rose*  pub- 
lished the  result  of  a  single  analysis  of  antimony  trichloride,  previously 
made  under  his  supervision  b}7  Weber.  This  analysis,  if  Cl  =  35.5,  makes 
Sb  =  120.7,  a  value  of  no  great  weight,  but  in  a  measure  confirmatory  of 
that  obtained  by  Schneider. 

The  next  research  upon  the  atomic  weight  of  antimony  was  that  of 
Dexter,f  published  in  1857.  This  chemist,  having  tried  to  determine 
the  amount  of  gold  precipitable  by  a  known  weight  of  antimony,  and 
having  obtained  discordant  results,  finally  resorted  to  the  original  method 
of  Berzelius.  Antimony,  purified  with  extreme  care,  was  oxidized  by 
nitric  acid,  and  the  gain  in  weight  was  determined.  From  1.5  to  3.3 
grammes  of  metal  were  used  in  each  experiment.  The  reduction  of  the 
weights  to  a  vacuum  standard  was  neglected  as  being  superfluous.  From 
the  data  obtained,  we  get  the  following  percentages  of  Sb  in  Sb.204 : 

79.268 
73.272 

79-255 
79.266 

79-253 
79.271 
79.264 
79.260 
79.286 

79-274 
79.232 

79-395 
79-379 


Mean,  79.283,  ±  .009 

Hence,  if  0  =  16,  Sb  =  122.46. 

The  determinations  of  Dumas  J  were  published  in  1859.  This  chemist 
sought  to  fix  the  ratio  between  silver  and  antimonious  chloride,  and  ob- 
tained results  for  the  atomic  weight  of  antimony  quite  near  to  those  of 
Dexter.  The  SbCl3  was  prepared  by  the  action  of  dry  chlorine  upon 
pure  antimony;  it  was  distilled  several  times  over  antimony  powder, 
and  it  seemed  to  be  perfectly  pure.  Known  weights  of  this  preparation 
were  added  to  solutions  of  tartaric  acid  in  water,  and  the  silver  chloride 
was  precipitated  without  previous  removal  of  the  antimony.  Here,  as 

*  Poggend.  Annalen,  98,  455.     1856. 
t  Poggend.  Annalen,  100,  363.     1857. 
I  Ann.  Chim.  Phys.  (3),  55,  175. 


218  THE    ATOMIC    WEIGHTS. 

Cooke  has  since  shown,  is  a  possible  source  of  error,  for  under  such 
circumstances  the  crystalline  argento-antimoiiious  tartrate  may  also  be 
thrown  down  and  contaminate  the  chloride  of  silver.  But  be  that  as  it 
may,  Dumas'  weighings,  reduced  to  a  common  standard,  give  as  propor- 
tional to  100  parts  of  silver,  the  quantities  of  SbCl3  which  are  stated  in 
the  third  of  the  subjoined  columns  : 

i.876grm.  SbCl3  =  2.66o  grm.  Ag.  70.526 

4.336  "  6.148         "  70.527 

5.065  "  7.175         "  70.592 

3-475  4-93°  "  70.487 

3.767  5.350  «  70.411 

5.910  "             8.393  "  70.416 

4.828  "             6.836  "  70.626 

Mean,  70.512,  ±  .021 

Hence,  if  Ag  =  108,  and  Cl  =  35,5,  Sb  =  122. 

In  1861  Kessler's  second  paper  *  relative  to  the  atomic  weight  of  an- 
timony appeared.  Kessler's  methods  were  somewhat  complicated,  and 
for  full  details  the  original  memoirs  must  be  consulted.  A  standard 
solution  of  potassium  dichromate  was  prepared,  containing  6.1466 
grammes  to  the  litre.  With  this,  solutions  containing  known  quantities 
of  antimony  or  of  antimony  compounds  were  titrated,  the  end  reaction 
being  adjusted  with  a  standard  solution  of  ferrous  chloride.  In  some 
cases  the  titration  was  preceded  by  the  addition  of  a  definite  weight  of 
potassium  chlorate,  insufficient  for  complete  oxidation ;  the  dichromate 
then  served  to  finish  the  reaction.  The  object  in  view  was  to  determine 
the  amount  of  oxidizing  agent,  and  therefore  of  oxygen,  necessary  for 
the  conversion  of  known  quantities  of  antimonious  into  antimonic  com- 
pounds. 

In  the  later  paper  Kessler  refers  to  his  earlier  work,  and  shows  that 
the  values  then  found  for  antimony  were  all  too  high,  except  in  the  case 
of  the  series  made  with  tartar  emetic.  That  series  he  merely  states,  and 
subsequently  ignores,  evidently  believing  it  to  be  unworthy  of  further 
consideration.  For  the  remaining  series  he  points  out  the  sources  of 
error.  These  need  not  be  rediscussed  here,  as  the  discussion  would  have 
no  value  for  present  purposes ;  suffice  it  to  say  that  in  the  series  repre- 
senting the  oxidation  of  Sb20s  with  dichromate  and  chlorate,  the  ma- 
terial used  was  found  to  be  impure.  Upon  estimating  the  impurity  and 
correcting  for  it,  the  earlier  value  of  Sb  =  123.80  becomes  Sb  =  122.36, 
according  to  Kessler's  calculations. 

In  the  paper  now  under  consideration  four  series  of  results  are  given. 
The  first  represents  experiments  made  upon  a  pure  antimony  trioxide 
which  had  been  sublimed,  and  which  consisted  of  shining  colorless 
needles.  This  was  dissolved,  together  with  some  potassium  chlorate,  in 

*Poggend.  Annalen,  113,  145.     1861. 


ANTIMONY.  219 

hydrochloric  acid,  and  titrated  with  dichromate  solution.  Six  experi- 
ments were  made,  but  Kessler  rejects  the  first  and  second  as  untrust- 
worthy. The  data  for  the  others  are  as  follows : 

S£2<93.  KCIO*.  K.jCr.jO^  sol.  in  cc. 

1,7888  grm.  .4527  grm.  19.200. 

1.6523    "  .45°6     "  3-9    " 

3.2998    "  .8806    "  16.5    " 

1.3438      "  .3492      "  10.2     " 

From  these  figures  Kessler  deduces  Sb  =  122.16. 

These  data,  reduced  to  a  common  standard,  give  the  following  quanti- 
ties of  oxygen  needed  to  oxidize  100  parts  of  Sb203  to  Sb2O5.  Each  cubic 
centimetre  of  the  K2Cr207  solution  corresponds  to  one  milligramme  of  0  : 

10.985 
10.939 
10.951 
10.936 


Mean,  10.953,  ±  -OO75 

In  the  second  series  of  experiments  pure  antimony  was  dissolved  in 
hydrochloric  acid  with  the  aid  of  an  unweighed  quantity  of  potassium 
chlorate.  The  solution,  containing  both  antimonious  and  antimonic 
compounds,  was  then  reduced  entirely  to  the  antimonious  condition  by 
means  of  stannous  chloride.  The  excess  of  the  latter  was  corrected  with 
a  strong  hydrochloric  acid  solution  of  mercuric  chloride,  then,  after 
diluting  and  filtering,  a  weighed  quantity  of  potassium  chlorate  was 
added,  and  the  titration  with  dichromate  was  performed  as  usual.  Cal- 
culated as  above,  the  percentages  of  oxygen  given  in  the  last  column 
correspond  to  100  parts  of  antimony: 

Sb.  KClOy  A"2Oa<97  sol.  cc.  Per  cent.  O. 

1.636  grm.  0.5000  grm.                       18.3                       13.088 

3.0825     "  0.9500    "                         30.2                     i3-°5° 

4.5652     "  1.4106     "                        45.5                      13.098 


Mean,  13.079,  ±  .0096 

This  series  gave  Kessler  Sb  =  122.34. 

The  third  and  fourth  series  of  experiments  were  made  with  pure 
antimony  trichloride,  SbCl3,  prepared  by  the  action  of  mercuric  chloride 
upon  metallic  antimony.  This  preparation,  in  the  third  series,  was  dis- 
solved in  hydrochloric  acid,  and  titrated.  In  one  experiment  solid 
K2O207  in  weighed  amount  was  added  before  titration;  in  the  other  two 
estimations  KC103  was  taken  as  usual.  The  third  column  gives  the 
percentages  of  oxygen  corresponding  to  100  parts  of  SbCl3. 


220  THE    ATOMIC    WEIGHTS. 

Per  cent.  O. 

1.8576  grm.  SbCl3  needed  .5967  grm.  K2Cr2O7  and  33.4  cc.  sol.     7.0338 
1.9118  "  .3019    "      KC1O3      "     16.2      "          7.0321 

4.1235  "  .6801     "      KC1O3      "     23.2      "          7.0222 

Mean,  7.0294,  ±  .0024 

The  fourth  set  of  experiments  was  gravimetric.  The  solution  of  Sb013 
mixed  with  tartaric  acid,  was  first  precipitated  by  hydrogen  sulphide, 
in  order  to  remove  the  antimony.  The  excess  of  H2S  was  corrected  by 
copper  sulphate,  and  then  the  chlorine  was  estimated  as  silver  chloride 
in  the  ordinary  manner.  100  parts  of  AgCl  correspond  to  the  amounts 
of  SbCl3  given  in  the  third  column. 

1.8662  grm.  SbCl3  gave  3.483  grm.  AgCl.  53-58o 

1.6832  «  3.141  "  53.588 

27437  5-IH5        "  53-677 

2.6798  5.0025        "  53.569 

5.047  9.411  53.629 

3.8975  "  7.2585         "  53.696 


Mean,  53.623,  =b  .015 

The  volumetric  series  with'SbC!3  gave  Kessler  values  for  Sb  ranging 
from  121.16  to  121.47.  The  gravimetric  series,  on  the  other  hand,  yielded 
results  from  Sb  =  124.12  to  124.67.  This  discrepancy  Kessler  rightly 
attributes  to  the  presence  of  oxygen  in  the  chloride;  and,  ingeniously 
correcting  for  this  error,  he  deduces  from  both  sets  combined  the  value  of 
Sb  =  122.37. 

The  several  mean  results  for  antimony  agree  so  fairly  writh  each  other, 
and  with  the  estimates  obtained  by  Dexter  and  Dumas,  that  we  cannot 
wonder  that  Kessler  felt  satisfied  of  their  general  correctness,  and  of  the 
inaccuracy  of  the  figures  published  by  Schneider.  Still,  the  old  series 
of  data  obtained  by  the  titration  of  tartar  emetic  with  dichromate  con- 
tained no  evident  errors,  and  was  not  accounted  for.  This  series,*  if 
we  reduce  all  of  Kessler's  figures  to  a  single  common  standard,  gives  a 
ratio  between  K2Cr207  and  C4H4KSb07.£H20.  100  parts  of  the  former 
will  oxidize  of  the  latter : 

336.64 

338.01 

336.83 

337-93 

338.59 

335;79 

Mean,  337.30,  ±  .29 

From  this,  if  K,Cr207=  292.271,  Sb  =  118.024. 

The  newer  atomic  weights  found  in  other  chapters  of  this  work  will 

*Poggend.  Annalen,  95,  217. 


ANTIMONY.  221 

be  applied  to  the  discussion  of  all  these  series  further  along.  It  may, 
however,  be  properly  noted  at  this  point  that  the  probable  errors  assigned 
to  the  percentages  of  oxygen  in  three  of  Kessler's  series  are  too  low. 
These  percentages  are  calculated  from  the  quantities  of  KC103  involved 
in  the  several  reactions,  and  their  probable  errors  should  be  increased 
with  reference  to  the  probable  error  of  the  molecular  weight  of  that  salt. 
The  necessary  calculations  would  be  more  laborious  than  the  importance 
of  the  figures  would  warrant,  and  accordingly,  in  computing  the  final 
general  mean  for  antimony,  Kessler's  figures  will  receive  somewhat  higher 
weight  than  they  are  legitimately  entited  to. 

Naturally,  the  concordant  results  of  Dexter,  Kessler,  and  Dumas  led 
to  the  general  acceptance  of  the  value  of  122  for  antimony  as  against  the 
lower  figure,  120,  of  Schneider.  Still,  in  1871,  linger  *  published  the  re- 
sults of  a  single  analysis  of  Schlippe's  salt,  Na3SbS4.9H20.  This  analysis 
gave  Sb  =  119.76.  if  S  =  32  and  Na  =  23,  but  no  great  weight  could  be 
attached  to  the  determination.  It  served,  nevertheless,  to  show  that  the 
controversy  over  the  atomic  weight  of  antimony  was  not  finally  settled. 

More  than  ten  years  after  the  appearance  of  Kessler's  second  paper  the 
subject  of  the  atomic  weight  of  antimony  was  again  taken  up,  this  time 
by  Professor  Cooke.  His  results  appeared  in  the  autumn  of  1877 1  and 
were  conclusive  in  favor  of  the  lower  value,  approximately  120.  For  full 
details  the  original  memoir  must  be  consulted ;  only  a  few  of  the  leading 
points  can  be  cited  here. 

Schneider  analyzed  a  sulphide  of  antimony  which  was  already  formed. 
Cooke,  reversing  the  method,  effected  the  synthesis  of  this  compound. 
Known  weights  of  pure  antimony  were  dissolved  in  hydrochloric  acid 
containing  a  little  nitric  acid.  In  this  solution  weighed  balls  of  antimony 
were  boiled  until  the  liquid  became  colorless  ;  subsequently  the  weight 
of  metal  lost  by  the  balls  was  ascertained.  To  the  solution,  which  now 
contained  only  antimonious  compounds,  tartaric  acid  was  added,* and 
then,  with  a  supersaturated  aqueous  sulphhydric  acid,  antimony  trisul- 
phide  was  precipitated.  The  precipitate  was  collected  by  an  ingenious 
process  of  reverse  filtration,  converted  into  the  black  modification  by 
drying  at  210°,  and  weighed.  After  weighing,  the  Sb.2S3  was  dissolved 
in  hydrochloric  acid,  leaving  a  carbonaceous  residue  unacted  upon. 
This  was  carefully  estimated  and  corrected  for.  About  two  grammes  of 
antimony  were  taken  in  each  experiment  and  thirteen  syntheses  were 
performed.  In  two  of  these,  however,  the  antimony  trisulphide  was 
weighed  only  in  the  red  modification,  and  the  results  were  uncorrected 
by  conversion  into  the  black  variety  and  estimation  of  the  carbonaceous 
residue.  In  fact,  every  such  conversion  and  correction  was  preceded  by 
a  weighing  of  the  red  modification  of  the  Sb,S3.  The  mean  result  of  these 
weighings,  if  S  —  32,  gave  Sb  =  119.994.  The  mean  result  of  the  cor- 

*  Archiv.  der  Pharmacie,  197,  194.     Quoted  by  Cooke. 
f  Proc.  Amer.  Acad.,  5,  13. 


222  THE    ATOMIC    WEIGHTS. 

reeled  syntheses  gave  Sb  =  120.295.     In  these  eleven  experiments  the 
following  percentages  of  S  in  SbaS3  were  established  : 

28.57 
28.60 
28.57 
28.43  • 
28.42 

28.53 
28.50 
28.49 
28.58 
28.50 
28.51 


Mean,  28.5182,  =b  .0120 

These  results,  confirmatory  of  the  work  of  Schneider,  were  presented 
to  the  American  Academy  in  1876.  Still,  before  publication,  Cooke 
thought  it  best  to  repeat  the  work  of  Dumas,  in  order  to  detect  the  cause 
of  the  old  discrepancy  between  the  values  Sb  =  120  and  Sb  =  122.  Ac- 
cordingly, various  samples  of  antimony  trichloride  were  taken,  and  puri- 
fied by  repeated  distillations.  The  final  distillate  was  further  subjected 
to  several  recrystallizations  from  the  fused  state ;  or,  in  one  case,  from  a 
saturated  solution  in  a  bisulphide  of  carbon.  The  portions  analyzed 
were  dissolved  in  concentrated  aqueous  tartaric  acid,  and  precipitated 
by  silver  nitrate,  many  precautions  being  observed.  The  silver  chloride 
was  collected  by  reverse  filtration,  and  dried  at  temperatures  from  110° 
to  120°.  In  one  experiment  the  antimony  was  first  removed  by  H2S. 
Seventeen  experiments  were  made,  giving,  if  Ag  =  108  and  Cl  =  35.5.  a 
mean  value  of  Sb  =  121.94.  If  we  reduce  to  a  common  standard,  Cooke's 
analyses  give,  as  proportional  to  100  parts  of  AgCl,  the  quantities  of  SbCls 
stated  in  the  third  column : 

i.5974grm.  SbCl3  gave  3.0124  grm.  AgCl.  53.028 

1.2533  "  2.3620  "                          53.061 

.8876  1.6754  52.978 

.8336  i  5674  53-^4 

.5326  "•  i. 0021  "                         53-H8 

.7270  "  i.369T  "                         53-T°i 

1.2679  "  2.3883  "                         53.088 

1.9422  3.6646  52.999 

1-7702  "  3-3384  "                         53.025 

2.5030  4-7184  53.048 

2.1450  "  4.0410  "                         53.081 

1.7697  "  3.3281  "                         53.175 

2-3435  4.4157  53.072 

1.3686  "  2.5813  "                        53-O2O 

1.8638  "  3-5'46  "                        53.03° 

2.0300  "  3.8282  "                        53.028 

2.4450  "  4.6086  «                        53.053 

Mean,  53  066,  zfc  .0096 


ANTIMONY. 


223 


This  mean  may  be  combined  with  that  of  Kessler's  series,  as  follows  : 

Kessler  .............  '  ................  .  ...  53.623,    d=  .015 

Cooke  ............  ----    ............  ____  53.o66,    ±  .0096 


General  mean  ...................  53.2311,  ±  .008 

The  results  thus  obtained  with  SbCl3  confirmed  Dumas'  determination 
of  the  atomic  weight  of  antimony  as  remarkably  as  the  syntheses  of  Sb2S3 
had  sustained  the  work  of  Schneider.  Evidently,  in  one  or  the  other 
series  a  constant  error  must  be  hidden,  and  much  time  was  spent  by 
Cooke  in  searching  for  it.  It  was  eventually  found  that  the  chloride  of 
antimony  invariably  contained  traces  of  oxychloride,  an  impurity  which 
tended  to  increase  the  apparent  atomic  weight  of  the  metal  under  con- 
sideration. It  was  also  found,  in  the  course  of  the  investigation,  that 
hydrochloric  acid  solutions  of  antimonious  compounds  oxidize  in  the  air 
during  boiling  as  rapidly  as  ferrous  compounds,  a  fact  which  explains 
the  high  values  for  antimony  found  by  Kessler. 

In  order  to  render  "assurance  doubly  sure."  Professor  Cooke  also 
undertook  the  analysis  of  the  bromide  and  the  iodide  of  antimony.  The 
bromide,  SbBrs,  was  prepared  by  adding  the  finely  powdered  metal  to  a 
solution  of  bromine  in  carbon  disulphide.  It  was  purified  by  repeated 
distillation  over  pulverized  antimony,  and  by  several  recrystallizations 
from  bisulphide  of  carbon.  The  bromine  determinations  resemble  those 
of  chlorine,  and  gave,  if  Ag  =  108  and  Br  =  80,  a  mean  value  for  anti- 
mony of  Sb  =  120.  Reduced  to  a  common  standard,  the  fifteen  analyses 
give  the  subjoined  quantities  of  SbBr3  proportional  to  100  parts  of  silver 
bromide  : 


1.8621  grm.  SbBr3  gave  2.9216  grm.  AgBr. 


.9856 
1.8650 
1.5330 
1.3689 
1.2124 

.9417 
2.5404 
1.5269 
1.8604 
1.7298 
3-2838 
2.3589 
L3323 
2.6974 


1.5422 
2.9268 
2.4030 

2.1445 
1.8991 
1.4749 
3-9755 
2.3905 
2.9180 
2.7083 
5.1398 
3.6959 
2.0863 
4.2285 


63-736 
63.909 
63.721 
63.795 
63-833 
63841 
63.848 
63.901 
63-874 
63-756 
63.870 
63.890 
63.825 
63-859 
63-791 

Mean,  63.830,  ±  .008 


The  iodide  of  antimony  was  prepared  like  the  bromide,  and  analyzed 
in  the  same  way.  At  first,  discordant  results  were  obtained,  due  to  the 
presence  of  oxyiodide  in  the  iodide  studied.  The  impurity,  however, 


224 


THE   ATOMIC    WEIGHTS. 


was  removed  by  subliming  the  iodide  in  an  atmosphere  of  dry  carboi 
dioxide.     With  this  purer  material,  seven  estimations  of  iodine  wei 
made,  giving,  if  Ag  =  108  and  I  =  127,  a  value  for  antimony  of  Sb  =  120. 
Reduced  to  a  uniform  standard,  Cooke's  weighings  give  the  following 
quantities  of  SbI3  proportional  to  100  parts  of  silver  iodide : 

1.1877  grm.  SbI3  gave  1.6727  grm.  Agl.       71.005 


.4610 

3.2527 
1. 8068 
1.5970 
2.3201 
•  3496 


.6497 


2.5389 
2.2456 


.4927 


70.956 
71.150 
71.165 
71.117 
71.071 
70.956 

Mean,  71.060,  ±  .023 


Although  Cooke's  work  was  practically  conclusive,  as  between  the  rival 
values  for  antimony,  his  results  were  severely  criticised  by  Kessler,*  who 
evidently  had  read  Cooke's  paper  in  a  very  careless  way.  On  the  other- 
hand,  Schneider  published  in  Poggendorff 's  Annalen  a  friendly  review 
of  the  new  determinations,  which  so  well  vindicated  his  own  accuracy. 
In  reply  to  Kessler,  Cooke  undertook  still  another  series  of  experiments 
with  antimony  bromide,f  and  obtained  absolute  confirmation  of  his 
previous  results.  To  a  solution  of  antimony  bromide  was  added  a  solu- 
tion containing  a  known  weight  of  silver  not  quite  sufficient  to  precipi- 
tate all  the  bromine.  The  excess  of  the  latter  was  estimated  by  titration 
with  a  normal  silver  solution.  Five  analyses  gave  values  for  antimony 
ranging  from  119.98  to  120.02,  when  Ag  =  108  and  Br  =  80.  Reduced 
to  a  common  standard,  the  weights  obtained  gave  the  amounts  of  SbBr 
stated  in  the  third  column  as  proportional  to  100  parts  of  silver : 

2.5032  grm.  SbBr3  =  2.2528  grm.  Ag. 
2.0567      "      1.8509 
2.6512      "      2.3860   " 
3-3°53      "      2.9749 


2.7495 


2-4745 


111.115 
111.119 
111.115 
111.106 
111.113 

Mean,  1 11.114,  ±  .0014 


Schneider^  also,  in  order  to  more  fully  answer  Kessler's  objections, 
repeated  his  work  upon  the  Arnsberg  stibmte.  This  he  reduced  in  hydro- 
gen as  before,  correcting  scrupulously  for  impurities.  The  following 
percentages  of  sulphur  were  found  : 

28.546 

28.534 
28.542 

Mean,  28  541,  db  .0024 

*Berichte  d.  Deutsch.  Chem.  Gesell.,  12,  1044.     1879. 

f  Amer.  Journ.  Sci.  and  Arts,  May,  1880.     Berichte,  13,  951. 

JJourn.  fur  Prakt.  Chem.  (2),  22,  131. 


ANTIMONY 


225 


These  figures  confirm  his  old  results,  and  may  be  fairly  combined  with 
them  and  with  the  percentages  found  by  Cooke,  as  follows : 

Schneider,  early  series 28.520,     ±  .008 

Schneider,  late  series 28.541,    ±  .0024 

Cooke 28.5182,  ±  .0120 


General  mean 28.5385,  =b  .0023 


In  1881  Pfeifer  *  determined  electrolytically  the  direct  ratios  between 
silver  and  antimony,  and  copper  and  antimony.  With  copper  the  fol- 
lowing data  were  obtained  : 


G/ 


1.412  grm, 

1.902 

3.367 


Sb  =  1.1008  Cu. 
1.4832    " 
2.6249    " 


Sb}  :  :  IOO 
128.270 
128.236 
128.272 


If  Cu  =  63.6,  Sb  =  122.36. 
With  silver  he  found — 


5.925  grm.  Sb=  15.774  Ag. 


6.429 
10.116 

4  865 
4.390 
9.587 
4.525 


17.109 
26.972 
13.014 
11.697 
25.611 
12.097 


Mean,  128.259,  ±  .0077 


Ag^  :  Sb  :  \  100  :  ,r. 
37.562 
37-577 
37.506 
37.383 
37-531 
37.433 
37.406 

Mean,  37.485,  d=  .0198 


If  Ag  =  108,  Sb  ==  121.45. 

The  latter  ratio  was  also  determined  by  Popper,  f  several  years  after- 
wards. The  two  metals  were  precipitated  simultaneously  by  the  same 
current ;  and  in  some  experiments  two  portions  of  antimony  were  thrown 
down  against  one  of  silver.  These  are  indicated  in  the  subjoined  table 
by  suitable  bracketing,  and  the  ratio  is  given  in  the  third  column  : 


Sb. 

Ag. 

Ratio. 

1.4856) 
1.4788  / 

3-9655 

37.463 
37.292 

2.OI2O  | 
2.OO74  ) 
3.88821 

3.8903  » 

5-3649 
10.3740 

37.503 
37.417 
37.48o 

37.50° 

4.1885  » 

11.1847 

37-455 
37-447 

*  Ann.  Chem.  Pharm.,  209,  161. 
t  Ann.  Chem.,  233,  153. 


15 


226  THE   ATOMIC    WEIGHTS. 


„  gfig  37.507 

4.2752  j  37.545 

5.6860  1  37.460 

5.6901  /  37.487 

4.4117  11.8014  37.383 

4.9999  13.3965  37.322 

5.2409  14.0679  37.250 

Mean,  37.434,  ±  .0149 
Pfeifer  found,  37.485,  ±  .0198 


General  mean,  37.452,  ±  .0119 

If  Ag  =  108,  Popper's  figures  give  in  mean  Sb  =  121.3. 

I  am  inclined  to  attach  slight  importance  to  these  electrolytic  data, 
for  the  reasons  that  it  would  be  very  difficult  to  ensure  the  absolute 
purity  and  freedom  from  occlusions  of  the  antimony  as  weighed,  or  to 
guarantee  that  no  secondary  reactions  had  modified  the  ratios. 

The  work  done  by  Bongartz  *  in  1883  was  quite  different  from  any  of 
the  determinations  which  had  preceded  it.  Carefully  purified 'antimony 
was  weighed  as  such,  and  then  dissolved  in  a  concentrated  solution  of 
potassium  sulphide.  From  this,  after  strong  dilution,  antimony  trisul- 
phide  was  thrown  down  by  means  of  dilute  sulphuric  acid.  After 
thorough  washing,  this  sulphide  was  oxidized  by  hydrogen  peroxide,  by 
Classen's  method,  and  the  sulphur  in  it  was  weighed  as  barium  sulphate. 
The  ratio  measured,  therefore,  was  2Sb  :  3BaS04,  and  the  data  were  as 
follows.  The  BaS04  equivalent  to  100  parts  of  Sb  is  the  ratio  stated  : 

Sb  Taken.  BaSO±  Found.  Ratio. 

1.4921  4.3325  290.362 

.6132  1.7807  290.394 

.5388  1.5655  290.553 

T.2II8  3.5205  290.518 

.9570  2.7800  290.491 

.6487  1.8855  290.349 

.7280  2. 1 100  289.835 

•  9535  2.7655  290.036 

I.O275  2.9800  290.024 

.9635  2.7980  290.399 

.9255  2.6865  290.275 

.7635  2.2175  290.438 


Mean,  290.306,  ±  .0436 

We  have  now  before  us  the  following  ratios,  good  and  bad,  from  which 
to  calculate  the  atomic  weight  of  antimony.  The  single  results  obtained 
by  Weber  and  by  Unger,  being  unimportant,  are  not  included  : 

*  Ber.  Deutsch.  Chem.  Gesell.,  16,  1942.     1883. 


ANTIMONY.  227 

(i.)  Percentage  of  S  in  Sb2S3,  28.5385,  ±  .0023 

(2.)  Percentage  of  Sb  in  Sb2O4,  79.283,  ±  .009 

(3.)  O  needed  to  oxidize  100  parts  SbCJ3,  7.0294,  ±  .0024 

(4.)  O  needed  to  oxidize  100  parts  Sb2O3,  10.953,  ±  -°O75 

(5.)  O  needed  to  oxidize  100  parts  Sb,  13.079,  Hh  .0096 

(6.)  K2Cr2O7  :  tartar  emetic  :  :  100  :  337.30,  ±  .29 

(7-)  ASs  '•  SbCl3  :  :  100  :  70.512,  ±  .021 

(8.)  3AgCl  :  SbG3  :  :  100  :  53.2311,  ±  .008 

(9-)  A§3  '•  SbBr3  :  :  loo  :  111.114,  ±  .0014 

(10.)  3AgBr  :  SbBr3  :  :  loo  :  63.830,  ±  .008 

(11.)  3AgI  :  SbI3  :  :  100  :  71.060,  ±  .023 

(12.)  Cu3  :  Sb2  :  :  100  :  128.259,  ±  .0077 

(T3-)  A£3  =  Sb  :  :  100  :  37.452,  ±  .0119 

(14.)  Sb2  :  3BaSO4  :  :  100  :  290.306,  rb  .0436 

In  the  reduction  of  these  ratios  a  considerable  number  of  antecedent 
atomic  weights  are  required,  thus  : 

0  =   15.879,  +  .0003  C       =   11.920,  ±  .0004 
Ag  =  107.108,  ±.0031  Cu      =    63.119,  ±  .0015 
cl  =::    35-179,  ±  .0048  Ba       =  136.392,  ±  .0086 
Br  ==    79-344,  ±  .0062  Cr       =    51.742,  ±  .0034 

1  =  125.888,^.0069  AgCl  =  142.287,  ±  .0037 
K    =  =    38.817,  ±  .0051  AgBr=r  186.452,  ±  .0054 
S     ;=    31.828,^.0015  Agl    =232.996,^3.0062 

Three  of  the  ratios  give  the  molecular  weight  of  antimony  trichloride, 
and  two  give  corresponding  values  for  the  bromide.  These  values  may 
be  combined,  as  follows  :  First,  for  the  chloride — 

From  (3) SbCl3  =  225.894,  ±  .0771 

From  (7) , "      =  226.572,  ±  .0678 

From  (8) "      =  227.223,  dr  .0347 


General  mean SbCl3  =  226.924,  ±  .0286 

Hence  Sb  =  121.387,  dr  .0321. 
For  the  bromide  we  have — 

From  (9) r.   SbBr3  —  357.036,  ±  .0113 

From  ( 10) "      =  357.037,  ±  .0250 


General  mean SbBr3  =  357.036,  ±  .0103 

Hence  Sb  =  119.005,  ±  .0212. 

All  the  data  yield  eleven  values  for  antimony,  which  are  arranged 
below  in  the  order  of  their  magnitude  : 


228  THE   ATOMIC   WEIGHTS. 

1.  From  tartar  emetic,  ratio  (6) Sb  =  118.024,  ±  .2827 

2.  From  SbBr3 "  =  119.005,  d=  .0212 

3.  From  SbI3,  ratio  (i i ) "=  119.037,  ±  .1626 

4.  From  Sb2S3,  ratio  (i) "  =  119.548,  ±  .0069 

5.  From  ratio  (14) "  =  119.737,  ±  .0188 

6.  From  ratio  (13) "  =  120.342,  ±  .0384 

7.  From  ratio  (4) "  =  121.155,  ±  .1000 

8.  From  SbCl3 "  =.  121.387,  ±  .0321 

9.  From  ratio  (5) "— 121.408,  ±  .0891 

10.  From  ratio  (12) "  =  121.434,  ±  .0078 

11.  From  Sb2O4,  ratio  (2) u  =  121.542,  ±  .0546 


General  mean Sb  =  120.299,  zb  .0047 

If  0  =  16,  this  becomes  Sb  =  121.218. 

Among  these  figures  the  discordance  is  so  great  that  the  mathematical 
combination  has  no  real  value.  We  must  base  our  judgment  in  this  case 
mainly  upon  chemical  evidence,  and  this,  as  shown  in  the  investigations 
of  Cooke  and  of  Schneider,  favors  a  lower  rather  than  a  higher  value  for 
the  atomic  weight  of  antimony.  Dumas'  work  was  affected  by  constant 
errors  which  are  now  known,  and  Dexter's  data  are  also  presumably  in 
the  wrong.  A  general  mean  of  values  2,  3,  4,  and  5  gives  Sb  =  119.521, 
±  .0062,  or,  if  0  =  16,  Sb  =  120.432.  Even  now  the  range  of  uncertainty 
is  greater  than  it  should  be,  but  none  of  the  four  values  combined  can 
be  accepted  exclusively  or  rejected  without  more  evidence.  This  result, 
therefore,  should  be  adopted  until  new  determinations,  of  a  more  con- 
clusive nature,  have  been  made. 


BISMUTH.  229 


BISMUTH. 

Early  in  the  century  the  combining  weight  of  bismuth  was  approxi- 
mately fixed  through  the  experiments  of  Lagerhjelm.*  Effecting  the 
direct  union  of  bismuth  and  sulphur,  he  found  that  ten  parts  of  the  metal 
yield  the  following  quantities  of  trisulphide : 

12.2520 
12.2065 
12.2230 
12.2465 


Mean,  12.2320 

Hence  Bi  =  215  in  round  numbers,  a  value  now  known  to  be  much  too 
high.  Lagerhjelm  also  oxidized  bismuth  with  nitric  acid,  and,  after  igni- 
tion, weighed  the  trioxide  thus  formed.  Ten  parts  of  metal  gave  the 
following  quantities  of  Bi203 : 

11.1382 
11.1275 

Mean,  11.13285 

Hence,  if  0  =  16,  Bi  =  211.85,  a  figure  still  too  high. 

In  1851  the  subject  of  the  atomic  weight  of  bismuth  was  taken  up  by 
Schneider,f  who,  like  Lagerhjelm,  studied  the  oxidation  of  the  metal 
with  nitric  acid.  The  work  was  executed  with  a  variety  of  experimental 
refinements,  by  means  of  which  every  error  due  to  possible  loss  of  mate- 
rial was  carefully  avoided.  For  full  details  the  original  paper  must  be 
consulted ;  there  is  only  room  in  these  pages  for  the  actual  results,  as 
follows.  The  figures  represent  the  percentages  of  Bi  in  Bi2O3 : 

89.652 
89.682 
89.644 
89.634 
89.656 
89.666 
89-655 
89-653 


Mean,  89.6552,  ±  .0034 

Hence,  if  0  =  16,  Bi  =  208.05. 

Next  in  order  are  the  results  obtained  by  Dumas.  J     Bismuth  tri- 

*  Annals  of  Philosophy,  4,  358.     1814.     Adopted  by  Berzelius. 
t  Poggend.  Annalen,  82,  303.     1851. 
I  Ann.  Chitn.  Phys.  (3),  55,  176.     1859. 


230  THE    ATOMIC    WEIGHTS. 

chloride  was  prepared  by  the  action  of  dry  chlorine  upon  bismuth,  and 
repeatedly  rectified  by  distillation  over  bismuth  powder.  The  product 
was  weighed  in  a  closed  tube,  dissolved  in  water,  and  precipitated  with 
sodium  carbonate.  In  the  filtrate,  after  strongly  acidulating  with  nitric 
acid,  the  chlorine  was  precipitated  by  a  known  amount  of  silver.  The 
figures  in  the  third  column  show  the  quantities  of  BiCl3  proportional  to 
100  parts  of  silver : 

98.90x3 

98-373 
98.005 
97.829 

97.996 
97.806 

97.643 
97.712 
97.762 


3.506  grm.  BiC 

H3  =  3.545  grm 

.  Ag. 

1.149           " 

1.168 

i  < 

1.5965 

1.629 

" 

2.1767 

2.225 

(  ( 

3.081 

3-H4 

" 

2.4158 

2.470 

it 

1.7107 

I-752 

n 

3.523 

3-6055 

i  < 

5.241 

5.36i 

" 

-     Mean,  98.003,  ±  .090 

Hence,  with  Ag  =  108  and  Cl  =  35.5,  Bi  =  211.03. 

The  first  three  of  the  foregoing  experiments  were  made  with  slightly 
discolored  material.  The  remaining  six  percentages  give  a  mean  of 
97.791,  whence,  on  the  same  basis  as  before,  Bi  =  110.79.  Evidently 
these  results  are  now  of  slight  value,  for  it  is  probable  that  the  chloride  of 
bismuth,  like  the  corresponding  antimony  compound,  contained  traces 
of  oxy chloride.  This  assumption  fully  accounts  for  the  discordance  be- 
tween Dumas'  determination  and  the  determinations  of  Schneider  and 
of  still  more  recent  investigators. 

In  1883  Marignac  *  took  up  the  subject,  attacking  the  problem  by  two 
methods.  His  point  of  departure  was  commercial  subnitrate  of  bismuth, 
which  was  purified  by  re-solution  and  reprecipitation,  and  from  which 
he  prepared  the  oxide.  First,  bismuth  trioxide  was  reduced  by  heating 
in  hydrogen,  beginning  with  a  moderate  temperature  and  closing  the 
operation  at  redness.  The  results  were  as  follows,  with  the  percentage 
of  Bi  in  Bi203  added : 

2.6460  grm.  Bi.2O3  lo^t  0.2730  grm.  O.  89.683  per  cent. 

6.7057  "  .6910        "  89.696       " 

3.6649  "  .3782        "  89.681        " 

5.8024  "  .5981         "  89.692        " 

5.1205  "  .5295        "  89.658        " 

5.5640  .5742        "  89.680       " 

Mean,  89.682,  i:  .0036 

Hence,  if  0  =  16,  Bi  =  208.60. 

*Arch.  Sci.  Phys.  et  Nat.  (3),  10,  10. 


BISMUTH.  231 

Marignac's  second  method  of  determination  was  by  conversion  of  the 
oxide  into  the  sulphate.  The  oxide  was  dissolved  in  nitric  acid,  and 
then  sulphuric  acid  was  added  in  slight  excess  from  a  graduated  tube. 
The  mass  was  evaporated  to  dryness  with  great  care,  and  finally  heated 
over  a  direct  flame  until  fumes  of  S03  no  longer  appeared.  The  third 
column  gives  the  sulphate  formed  from  100  parts  of  oxide : 

2.6503  Bi2O3  gave  4.0218  Bi2(SO4)3.  Ratio,  151.749 

2.8025           «          4.2535        "  "       151.775 

2.710                        4.112          "  "       I5L734 

2.813            "         4-267         "  "      151.688 

2.8750                     4.3625       "  ".      I5I-739 

2.7942          "         4-2383       "  "      151.682 


Mean,  151.728,  ±  .0099 

Hence,  with  O  =  16  and  S  =  32.06,  Bi  =  208.16. 

This  result  needs  to  be  studied  in  the  light  of  Bailey's  observation,* 
that  bismuth  sulphate  has  a  very  narrow  range  of  stability.  It  loses  the 
last  traces  of  free  sulphuric  acid  at  405°,  and  begins  to  decompose  at  418°, 
so  that  the  foregoing  ratio  is  evidently  uncertain.  The  concordance  of 
the  data,  however,  is  favorable  to  it. 

The  next  determination  of  this  atomic  weight  was  by  L6we,f  who 
oxidized  the  metal  with  nitric  acid,  and  reduced  the  nitrate  to  oxide  by 
ignition.  Special  care  was  taken  to  prepare  bismuth  free  from  arsenic, 
and  the  oxide  was  fused  before  weighing.  In  the  paper  just  quoted 
Bailey  calls  attention  to  the  volatility  of  bismuth  oxide,  which  doubt- 
less accounts  for  the  low  results  found  in  this  investigation.  The  data 
are  as  follows : 

Bi  Taken.  Bi^O^  Found.  Per  cent.  Bi. 

11.309  12.616  89.640 

12.2776  !3'694  89.656 


Mean,  89.648,  ±  .0040 

Hence,  if  0  =  16,  Bi  =  207.84. 

In  Classen's  J  work  upon  the  atomic  weight  of  bismuth,  the  metal 
itself  was  first  carefully  investigated.  Commercial  samples,  even  those 
which  purported  to  be  pure,  were  found  to  be  contaminated  with  lead 
and  other  impurities,  and  these  were  not  entirely  removable  by  many 
successive  precipitations  as  subnitrate.  Finally,  pure  bismuth  was  ob- 
tained by  an  electrolytic  process,  and  this  was  converted  into  oxide  by 
means  of  nitric  acid  and  subsequent  ignition  to  incipient  fusion.  Results 
as  follows,  with  the  percentage  of  Bi  in  Bi2O3  added : 

*  Journ.  Chem.  Soc.,  51,  676. 
tZeit.  Anal.  Chem.,  22,  498. 
\  Ber.  Deutsch.  Chem.  Gesell.,  23,  938.  1890. 


232  THE   ATOMIC    WEIGHTS. 

Bi  Taken.  Bi^Oz  Found.       Per  cent.  Bi. 

25.0667  27.9442  89.703 

21.0691  23.4875  89.7035 

27.2596  30.3922  89.693 

36.5195  40.713^  89.700 

27.9214  3H295  89.6944 

32.1188  35-8103  89.692 

30.1000  33.5587  89.694 

26.4825  59.5257  89.693 

19.8008  22.0758  89.695 


Mean,  89.696,  ±  .0009 

Hence,  if  0  ==  16,  Bi  =  208.92,  or,  reduced  to  vacuum  standards,  208.90. 

Classen's  paper  was  followed  by  a  long  controversy  between  Schneider 
and  Classen,*  in  which  the  former  upheld  the  essential  accuracy  of  the 
work  done  by  Marignac  and  himself.  Schneider  had  started  out  with 
commercial  bismuth,  and  Classen  found  that  the  commercial  bismuth 
which  he  met  with  was  impure.  Schneider,  by  various  analyses,  showed 
that  other  samples  of  bismuth  were  so  nearly  pure  that  the  common 
modes  of  purification  were  adequate  ;  but  Classen  replied  that  the  original 
sample  used  by  Schneider  in  his  atomic  weight  investigation  had  not 
been  reexamined.  Accordingly,  Schneider  published  a  new  series  of 
determinations  f  made  by  the  old  method,  but  with  metal  which  had 
been  scrupulously  purified.  Results  as  follows  : 

Bi.  Bi^.                        Percent.  Bi. 

5.0092  5.5868  89.661 

3.6770  4.1016  89.648 

7.2493  8.0854  89.659 

9.2479  10.3142  89.662 

6.0945  6.7979  89.653 

12.1588  13.5610  89.660 


Mean,  89.657,  ±  .0015 

Hence  with  O  =  16,  Bi  =  208.05,  a  confirmation  of  the  earlier  deter- 
minations. 

Although  the  results  so  far  are  not  final,  a  combination  of  the  data 
relative  to  bismuth  oxide  is  not  without  interest. 

1.  Lagerhjelm  ..........................   89.865,  db  .0650 

2.  Schneider,  185  1  .................  .....   89.655,  =b  .0034 

3.  Marignac  ............................   89.682,  ±  .0036 

4.  Lowe  ...............................   89.648,  ±  .0040 

5.  Classen   ...........................   89.  696,  ±  .0009 

6.  Schneider,  1894  ......................   89.657,  ±  .0015 


General  mean 89.681,  rb  .0007 


*  Journ.  fiir  Prakt.  Chem.  (2),  42,  553  ;  43,  133  ;  and  44,  23  and  411. 
t  Journ.  fiir  Prakt.  Chem.  (2),  50,  461.     1894. 


BISMUTH.  233 

Omitting  the  first  and  fifth  means,  the  other  data  give  a  general  mean 
percentage  of  89.659,  ±  .0012. 

The  ratios  now  before  us  are  as  follows : 

(I.)  Percentage  of  Hi  in  Bi2O3,  89.681,  ±  .0007 
(2.)  Bi2O3  :  Bi2(SO4)3  :  :  100  :  151.728,  ±  .0099 
13.)  3Ag  :  BiCl3  :  :  100  :  98.003,  ±  .090 

For  computation  we  have — 

O  =  15.879,  =b  .0003  Ag  =  107. 108,  zh  .0031 

8=31.828,^.0015  Cl  =    35.179,  ±.0048 

Hence,  reducing  the  ratios — 

From  (i) Bi  =  207.003,  ±  .0150 

From  (2)  ....    "  =  206.613,  ±  -°444 

From  (3) "  =  209.370,  ±  .2847 

General  mean Bi  =  206.971,  =b  .0142 

If  O  =  16,  Bi  =  208.548. 

Classen's  data  alone  give  Bi  =  207.389,  or,  with  0  =  16,  208.969. 
Omitting  this  set  of  determinations  and  rejecting  Dumas',  the  remaining 
data  give — 

From  Bi2O3 Bi  —  206.512,  ±  .0244 

From  Bi2(SO4)3 "  =  206.613,  ±  .0444 


General  mean Bi  =  206.536,  ±  .0214 

If  0  =  16,  this  becomes  Bi  =  208.11.  Between  this  figure  and  Classen's, 
future  investigation  must  decide.  The  confirmation  afforded  by  the 
sulphate  series  is  in  favor  of  the  lower  value. 


234  THE   ATOMIC    WEIGHTS. 


COLUMBIUM.* 

The  atomic  weight  of  this  metal  has  been  determined  by  Rose,  Her- 
mann, Blomstrand,  and  Marignac.  Rosef  analyzed  a  compound  which 
he  supposed  to  be  chloride,  but  which,  according  to  Rammelsberg,  J  must 
have  been  nearly  pure  oxychloride.  If  it  was  chloride,  then  the  widely 
varying  results  give  approximately  Cb  =  122  ;  if  it  was  oxychloride,  the 
value  becomes  nearly  94.  If  it  was  chloride,  it  was  doubtless  contami- 
nated with  tantalum  compounds. 

Hermann's  §  results  seem  to  have  no  present  value,  and  Blomstrand's  || 
are  far  from  concordant.  The  latter  chemist  studied  columbium  penta- 
chloride  and  sodium  columbate.  In  the  first  case  he  weighed  the  colum- 
bium as  columbium  pentoxide,  and  the  chlorine  as  silver  chloride,  the 
oxide  being  determined  by  several  distinct  processes.  In  some  cases  it 
was  thrown  down  by  water,  in  others  by  sulphuric  acid,  and  in  still 
others  by  sodium  carbonate  or  ammonia  jointly  with  sulphuric  acid.  The 
weights  given  are  as  follows  : 


Cb.,0,.  AgCl. 

•591  -294  ..... 

.8085  .401  2.085 

•633  .317  ..... 

.195  .0974  .500 

.507  .2505  1.302 

.9415  -472  2.454 

.563  .2796  ..... 

.9385  .4675  2.465 

.4788  .2378 

.408  .204  1.067 

•9065  .4515 

Hence  the  subjoined  percentages,  and  the  ratios  5AgCl  :  CbCl5  :  :  100  :  x, 
and  5  AgCl  :  Cb2O5  :  :  100  :  x. 


Percent.  C62<95. 

AgCl  :  CbCl,. 

AgCl  :  Ct>,0,. 

40  788 

T"-7     / 

49.598 

38-777 

19.233 

50.079 



49-949 

39.000 

19-435 

49.408 

38.940 

19.240 

50.135 

38.366 

19-234 

*This  name  has  priority  over  the  more  generally  accepted  "  niobium,"  and  therefore  deserves 
preference. 

fPoggend.  Annal.,  104,  439.     1858. 
JPoggend.  Annal.,  136,353.     r86g. 
I  Journ.  fiir  Prakt.  Chem.,  68,  73.     1856. 
|  Acta  Univ.  Lund.  1864. 


COLUMBIUM.  235 

49.662  ......  ...... 

49.813  38-073  18.966 

49.666  ......  ...... 

50.000  38-238  19.119 

49.807 


Mean,  49.806,  zh  .045        Mean,  38.566,  ±  .108      Mean,  19.205,  ±  .043 

From  these  means  the  atomic  weight  of  columbium  may  be  computed, 
thus: 

From  2CbCl5  :  Cb2O5  ........................   Cb  —  95.397 

From  CbCl5  :  5AgCl  ........................    "•;==  98.477 

From  5AgCl  :  Cb2O5  ........................    «  =  96.933, 

when  0  ==  15,879,  Ag  =  107.108,  and  Cl  =  35.179. 

The  series  upon  sodium  columbate,  which  salt  was  decomposed  with 
sulphuric  acid,  both  Cb205  and  Na2S04  being  weighed,  is  too  discordant 
for  discussion.  The  exact  nature  of  the  salt  studied  is  not  clear,  and  the 
data  given,  when  transformed  into  the  ratio  Na2SO4  :  Cb206  :  :  100  :  a;,  give 
values  for  x  ranging  from  151.65  to  161.20.  Further  consideration  of  this 
series  would  therefore  be  useless.  It  seems  highly  probable  that  Blom- 
strand's  materials  were  not  entirely  free  from  tantalum,  however,  since 
the  atomic  weight  of  columbium  derived  from  his  analyses  of  the  chloride 
are  evidently  too  high. 

Marignac*  made  about  twenty  analyses  of  the  potassium  nuoxy  colum- 
bate, CbOF3.2KF.H2O.  100  parts  of  this  salt  give  the  following  percent- 
ages : 

Cb2O5  ............  Extremes  44.15  to  44.60         Mean,  44.36 

K2SO,...  .........  ««          57.60-58.05 

H20  .............  "  5.75  "     5.98 

F  ................          "          30.62  "  32.22 

From  the  mean  percentage  of  Cb2O5,  Cb  =  92.852.  If  0  =  16,  this 
becomes  93.56. 

From  the  mean  between  the  extremes  given  for  K2S04,  Cb  =  93.192. 
If  0  =  16,  this  becomes  93.90. 

As  Beville  ami  Troost'sf  results  for  the  vapor  density  of  the  chloride 
and  oxychloride  agree  fairly  well  with  Cb  =  94,  we  may  adopt  this  value 
as  approximately  correct.  The  mean  of  the  two  values  computed  from 
Marignac's  data  is  93.022  when  H  =  1,  and  93.73  when  0  ==  16. 

*  Arch.  Sci.  Phys.  Nat.  (2),  23.     1865. 
f  Compt.  Rend.,  56,  891.     1863. 


236  THE    ATOMIC    WEIGHTS. 


TANTALUM. 

The  results  obtained  for  the  atomic  weight  of  this  metal  by  Berzelius,* 
Rose,f  and  Hermann  J  may  be  fairly  left  out  of  account  as  valueless. 
These  chemists  could  not  have  worked  with  pure  preparations,  and  their 
data  are  sufficiently  summed  up  in  Becker's  "  Digest." 

Blomstrand's  determinations,  §  as  in  the  case  of  columbium,  were 
made  upon  the  pentachloride.  His  weights  are  as  follows  : 


Ta.2Or,.  AgCl. 

.9808  .598  ...... 

1.4262  .867  2.906 

2.5282  1.5375  5.0105 

1.0604  .6455  2.156 

2.581  i.577  ...... 

•8767  -534 

Hence  the  subjoined  percentages  of  Ta205  from  TaCl5,  and  the  ratios 
SAgCl  :  TaCl5  :  :  100  :  x,  and  5AgCl  :  Ta205  :  :  100  :  x. 

Percent.  Ta,O5.  AgCl  :  TaCly  AgCl  :  Ta,O-0. 

60.971  ......  f   ...... 

60.791  49.078  29.835 

60.814  50.458  30685 

60.873  49.297  29.940 

60.960  ......  ...... 

60.924  ...... 


Mean,  60.889,  ±  .0208  49-6ir,  =b  .289  30.153,  dr  .180 

From  these  ratios  we  get  for  the  atomic  weight  of  tantalum  : 

From  per  cent.  Ta2O5 Ta  =  172.342 

From  5AgCl  :  TaCl5 ; "  =  177.055 

From  5  AgCl  :  Ta2O5 "  =174.821 

These  results  are  too  low.  Probably  Blomstrand's  material  still  con- 
tained some  columbium. 

In  1866  Marignac's  determinations  appeared. ||  He  made  four  analyses 
of  a  pure  potassium  fluotantalate,  and  four  more  experiments  upon  the 
ammonium  salt.  The  potassium  compound,  K2TaF7,  was  treated  with 
sulphuric  acid,  and  the  mixture  was  then  evaporated  to  dryness.  The 
potassium  sulphate  was  next  dissolved  out  by  water,  while  the  residue 

*  Poggend.  Annalen,  4,  14.     1825. 

f  Poggend.  Annalen,  99,  80.     1856. 

1  Journ.  fur  Prakt.  Chem.,  70,  193.     1857. 

g  Acta  Univ.  I^und,  1864 

||  Arch.  Sci.  Phys.  Nat.  (2),  26,  89.     1866. 


TANTALUM. 


237 


was  ignited  and  weighed  as  Ta205.     100  parts  of  the  salt  gave  the  follow- 
ing quantities  of  Ta2O5  and  K2S04 : 


56.50 
56.75 
56.55 
56.56 

Mean,  56.59,  ±  .037 


44-37 
44-35 
44.22 
44.24 


Mean,  44.295,  ±  .026 


From  these  figures,  100  parts  of  K2S04  correspond  to  the  subjoined 
quantities  of  Ta205 : 

127.338 
127.960 
128.178 
127.848 

Mean,  127.831,  ±  .120 

The  ammonium  salt,  (NH4)2TaF7,  ignited  with  sulphuric  acid,  gave 
these  percentages  of  Ta2O5.  The  figures  are  corrected  for  a  trace  of  K2SO4 
which  was  always  present : 

63.08 

63.24 

63.27 

63.42 

Mean,  63.25,  ±  .047 

Hence  we  have  four  values  for  Ta : 

From  potassium  salt,  per  cent.  Ta2O5 Ta  =  182.336 

From  potassium  salt,  per  cent.  K2SO4 "    —  180.496 

From  potassium  salt,  K2SO4  :  Ta2O5 "    —  181.422 

From  ammonium  salt,  per  cent.  Ta2O5 "    =  181.559 

Average Ta  =  181.453 


'Or,  if  0  =  16,  Ta  =  182.836. 
These  values  are  computed  with  O 
N  =  13.935,  and  F  =  18.912. 


15.879,  K  =  38.817,  S  =  31.828, 


238  THE    ATOMIC   WEIGHTS. 


CHROMIUM. 

Concerning  the  atomic  weight  of  chromium  there  has  been  much  dis- 
cussion, and  many  experimenters  have  sought  to  establish  the  true 
value.  The  earliest  work  upon  it  having  any  importance  was  that  of 
Berzelius,*  in  1818  and  1826,  which  led  to  results  much  in  excess  of  the 
correct  figure.  His  method  consisted  in  precipitating  a  known  weight 
of  lead  nitrate  with  an  alkaline  chromate  and  weighing  the  lead  chro- 
mate  thus  produced.  The  error  in  his  determination  arose  from  the  fact 
that  lead  chromate,  except  when  thrown  down  from  very  dilute  solu- 
tions, carries  with  it  minute  quantities  of  alkaline  salts,  and  so  has  its 
apparent  weight  notably  increased.  When  dilute  solutions  are  used,  a 
trace  of  the  precipitate  remains  dissolved,  and  the  weight  obtained  is  too 
low.  In  neither  case  is  the  method  trustworthy. 

In  1844  Berzelius'  results  were  first  seriously  called  in  question.  The 
figure  for  chromium  deduced  from  his  experiments  was  somewhat  over 
56 ;  but  Peligot  f  now  showed,  by  his  analyses  of  chromous  acetate  and 
of  the  chlorides  of  chromium,  that  the  true  number  was  near  52.5. 
Unfortunately,  Peligot's  work,  although  good,  was  published  with  in- 
sufficient details  to  be  useful  here.  For  chromous  acetate  he  gives  the 
percentages  of  carbon  and  hydrogen,  but  not  the  actual  weights  of  salt, 
carbon  dioxide,  and -water  from  which  they  were  calculated.  His  figures 
vary  considerably,  moreover — enough  to  show  that  their  mean  would 
carry  but  little  weight  when  combined  with  the  more  explicit  data  fur- 
nished by  other  chemists. 

Jacquelain's  £  work  we  may  omit  entirely.  He  gives  an  atomic  weight 
for  chromium  which  is  notoriously  too  low  (50.1),  and  prints  none  of  the 
numerical  details  upon  which  his  result  rests.  The  researches  which 
particularly  command  our  attention  are  those  of  Berlin,  Moberg,  Lefort, 
Wildenstein,  Kessler,  Siewert,  Baubigny,  Rawson,  and  Meineke. 

Among  the  papers  upon  the  atomic  weight  under  consideration  that 
by  Berlin  is  one  of  the  most  important.  §  His  starting  point  was  normal 
silver  chromate;  but  in  one  experiment  the  dichromate  Ag.2Cr,07  was 
used.  These  salts,  which  are  easily  obtained  in  a  perfectly  pure  condi- 
tion, were  reduced  in  a  large  flask  by  means  of  hydrochloric  acid  and 
alcohol.  The  chloride  of  silver  thus  formed  was  washed  by  decantation, 
dried,  fused,  and  weighed  without  transfer.  The  united  washings  were 
supersaturated  with  ammonia,  evaporated  to  dry  ness,  and  the  residue 
treated  with  hot  water.  The  resulting  chromic  oxide  was  then  collected 
upon  a  filter,  dried,  ignited,  and  weighed.  The  results  were  as  follows : 

*Schweigg.  Journ.,  22,  53,  and  Poggend.  Annal.,  8,  22. 

fCompt.  Rend.,  19,  609,  and  734;  20,  1187  ;  21,  74. 

I  Compt.  Rend.,  24,  679.     1847. 

f  Journ.  fur  Prakt.  Chem.,  37,  509,  and  38,  149.     1846. 


CHROMIUM.  239 

4.6680  grm.  Ag2CrO4  gave  4.027  grm.  AgCl  and  1.0754  grm.  Cr2O3. 
3.4568  "  2.983  "  .7960 

2.5060  "  2.1605  "  .5770         " 

2.1530  "  1.8555  "  -4945 

4-3335  grm-  Ag2Cr2O7  gave  2.8692  i.53°°         " 

From  these  weighings  three  values  are  calculable  for  the  atomic  weight 
of  chromium.  The  three  ratios  upon  which  these  values  depend  we  will 
consider  separately,  taking  first  that  between  the  chromic  oxide  and  the 
original  silver  salt.  In  the  four  analyses  of  the  normal  chromate  the 
percentages  of  Cr203  deducible  from  Berlin's  weighings  are  as  follows : 


Mean,  23.014,  =fc  .on 

And  from  the  single  experiment  with  Ag2Cr207  the  percentage  of  Cr2O, 
was  35.306. 

For  the  ratio  between  Ag2Cr04  and  AgCl,  putting  the  latter  at  100,  we 
have  for  the  former  : 

115-917 
115.883 
115.992 
116.033 


Mean,  115.956,  rb  .023 

In  the  single  experiment  with  dichromate  100  AgCl  is  formed  from 
151.035  Ag.2Cr2O7. 

Finally,  for  the  ratio  between  AgCl  and  Cr203,  the  five  experiments  of 
Berlin  give,  for  100  parts  of  the  former,  the  following  quantities  of  the 
latter : 

26.705 

26.685 

26.707 

26.650 

26.662 

Mean,  26.682,  ±  .0076 

These  results  will  be  discussed,  in  connection  with  the  work  of  other 
investigators,  at  the  end  of  this  chapter. 

In  1848  the  researches  of  Moberg*  appeared.  His  method  simply 
consisted  in  the  ignition  of  anhydrous  chromic  sulphate  and  of  am- 
monium chrome  alum,  and  the  determination  of  the  amount  of  chromic 

*  Journ.  fi'ir  Prakt.  Cheni.,  43,  114. 


240  THE   ATOMIC    WEIGHTS. 

oxide  thus  left  as  residue.  In  the  sulphate,  Cr2(S04)3,  the  subjoined  per- 
centages of  Cr203  were  found.  The  braces  indicate  two  different  sam- 
ples of  material,  to  which,  however,  we  are  justified  in  ascribing  equal 
value : 

.542  grm.  sulphate  gave  .212  grm.  Cr2O3.  39.114  per  cent.  ~\ 

1.337  "  .523         "  39.117       " 

.5287  .207     "  39. 153    "     3 

1.033  .406         "  39o03       "  ) 

.868  "  .341         "  39-286       " 


Mean,  39.1946,  ±  .0280 

From  the  alum,  NH4.Cr(S04)2.12H20,  we  have  these  percentages  of 
O2O3.  The  first  series  represents  a  salt  long  dried  under  a  bell  jar  at  a 
temperature  of  18°.  The  crystals  taken  were  clear  and  transparent,  but 
may  possibly  have  lost  traces  of  water,*  which  would  tend  to  increase 
the  atomic  weight  found  for  chromium.  In  the  second  series  the  salt  was 
carefully  dried  between  folds  of  filter  paper,  and  results  were  obtained 
quite  near  those  of  Berlin.  Both  of  these  series  are  discussed  together, 
neither  having  remarkable  value: 

1.3185  grm.  alum  gave  .213  grm.  Cr2O3.  1^>155  Per  cent. 

.7987  "  .129  "  1 6. 151  " 

1.0185  "  .1645  "  16.151  " 

1.0206  .1650  "  16.167  " 

.8765  .1420  "  16.201  " 

.7680  "  .1242  "  16.172  " 

1.6720  "  .2707  "  16.190  " 

.5410  .0875  <(  16.174 

1.2010  "  .1940  "  T6.i53  " 

i. ooio  "  .1620  "  16.184  " 

.7715  "  .1235  "  16.007 

1.374  "  .2200  "  16.012          " 


Mean,  16.143,  ±  .0125 

The  determinations  made  by  Lefortf  are  even  less  valuable  than  those 
by  Moberg.  This  chemist  started  out  from  pure  barium  chromate,  which, 
to  thoroughly  free  it  from  moisture,  had  been  dried  for  several  hours  at 
250°.  The  chromate  was  dissolved  in  pure  nitric  acid,  the  barium  thrown 
down  by  sulphuric  acid,  and  the  precipitate  collected  upon  a  filter,  dried, 
ignited,  and  weighed  in  the  usual  manner.  The  natural  objection  to  the 
process  is  that  traces  of  chromium  may  be  carried  down  with  the  sul- 
phate, thus  increasing  its  weight.  In  fact,  Lefort's  results  are  somewhat 
too  high.  Calculated  from  his  weighings,  100  parts  of  BaS04  correspond 
to  the  amounts  of  BaCr04  given  in  the  third  column : 


*  This  objection  is  suggested  by  Berlin  in  a  note  upon  Ivefort's  paper.     Journ.  fur  Prakt.  Chem. 
71,  191. 
t  Journ.  fur  Prakt.  Chem.,  51,  261.     1850. 


CHROMIUM.  241 

1.2615  grm-  BaCrO4  gave  1.1555  grm-  BaSO4.  109.174 

1.5895  "       L458o  "  109.019 

2.3255  "       2.1340  «  108.974 

3.0390  2.7855  "  109.101 

2.3480  2.1590  "  108.754 

1.4230  1.3060  u  108.708 

I.I975  1.1005  108.814 

3.4580  "       3-1690  "  109.119 

2.0130  1.8430  "  109.224 

3.5570  "       3-2710  "  108.744 

1.6470  "       1.5060  "  109.363 

1.8240  1-6725  "  109.058 

1.6950  "       1.5560  "  108.933 

2.5960  "       2.3870  "  108.756 


Mean,  108.9815,  ±  .0369 

Wildenstein,*  in  1853,  also  made  barium  chromate  the  basis  of  his 
researches.  A  known  weight  of  pure  barium  chloride  was  precipitated 
by  a  neutral  alkaline  chromate,  and  the  precipitate  allowed  to  settle  until 
the  supernatant  liquid  was  perfectly  clear.  The  barium  chromate  was 
then  collected  on  a  filter,  washed  with  hot  water,  dried,  gently  ignited, 
and  weighed.  Here  again  arises  the  objection  that  the  precipitate  may 
have  retained  traces  of  alkaline  salts,  and  again  we  find  deduced  an 
atomic  weight  which  is  too  high.  One  hundred  parts  BaCr04  correspond 


to  BaCl2  as  follows  : 


81.87  81.57 

81.80  81.75 
81.61  81.66 
81.78  81.83 
81.52  81.66 

81.84  81.80 

81.85  81.66 
81.70  81.85 
81.68  81.57 

81.54  81.83 
81.66  81.71 

81.55  81.63 

81.81  81.56 

81.86  81.58 
81.54  81.67 
81.68  81  84 


Mean,  81.702,  ±  .014 

Next  in  order  we  have  to  consider  two  papers  by  Kessler,  who  em- 
ployed a  peculiar  volumetric  method  entirely  his  own.  In  brief,  he  com- 
pared the  oxidizing  power  of  potassium  dichromate  with  that  of  the 
chlorate,  and  from  his  observations  deduced  the  ratio  between  the  mo- 
lecular weights  of  the  two  salts. 


t  Journ.  fiir  Prakt.  Chem.,  59,  27. 

16 


242  THE    ATOMIC    WEIGHTS. 

Iii  his  earlier  paper*  the  mode  of  procedure  was  about  as  follows: 
The  two  salts,  weighed  out  in  quantities  having  approximate  chemical 
equivalency,  were  placed  in  two  small  flasks,  and  to  each  was  added 
100  cc.  of  a  ferrous  chloride  solution  and  30  cc.  hydrochloric  acid.  The 
ferrous  chloride  was  added  in  trifling  excess,  and,  when  action  ceased, 
the  amount  unoxidized  was  determined  by  titration  with  a  standard  solu- 
tion of  dichrpmate.  As  in  each  case  the  quantity  of  ferrous  chloride  was 
the  same,  it  became  easy  to  deduce  from  the  data  thus  obtained  the  ratio 
in  question.  I  have  reduced  all  of  his  somewhat  complicated  figures  to 
a  simple  common  standard,  and  give  below  the  amount  of  chromate 
equivalent  to  100  of  chlorate : 

120.118 

120.371 

120.138 

120.096 

120.241 

120.181 


Mean,  120.191,  ±  .028 

In  his  later  paper  f  Kessler  substituted  arsenic  trioxide  for  the  iron 
solution.  In  one  series  of  experiments  the  quantity  of  dichromate  needed 
to  oxidize  100  parts  of  the  arsenic  trioxide  was  determined,  and  in  an- 
other the  latter  substance  was  similarly  compared  with  'the  chlorate. 
The  subjoined  columns  give  the  quantity  of  each  salt  proportional  to  100 
of  As203  : 


Mean,  99.045,  ±  .028 


Mean,  41.172,  ±  .009 

Reducing  the  later  series  to  the  standard  of  the  earlier,  the  two  com- 
bine as  follows  : 

'(l)   2KC1O3  :  K2Cr2O7  :  :  100  :  120.191,  ±  .028 
(2)   2KC1O3  :  K2Cr2O7  :  :  100  :  120.282,  ±  .043 

General  mean  ......     120.216,  ±  .0235 

*Poggend.  Annalen,  95,  208      1855. 
fPoggend.  Annalen,  113,  137.     1861. 


CHROMIUM.  243 

Siewert's  determinations,  which  do  not  seem  to  have  attracted  general 
attention,  were  published  in  1861.*  He,  reviewing  Berlin's  work,  found 
that  upon  reducing  silver  chromate  with  hydrochloric  acid  and  alcohol, 
the  chromic  chloride  solution  always  retained  traces  of  silver  chloride 
dissolved  in  it.  These  could  be  precipitated  by  dilution  with  water ; 
but,  in  Berlin's  process,  they  naturally  came  down  with  the  chromium 
hydroxide,  making  the  weight  of  the  latter  too  high  ;  hence  too  large  a 
value  for  the  atomic  weight  of  chromium.  In  order  to  find  a  more  cor- 
rect value  Siewert  resorted  to  the  analysis  of  sublimed,  violet,  chromic 
chloride.  This  salt  he  fused  with  sodium  carbonate  and  a  little  nitre, 
treated  the  fused  mass  with  water,  and  precipitated  from  the  resulting 
solution  the  chlorine  by  silver  nitrate  in  presence  of  nitric  acid.  The 
weight  of  the  silver  chloride  thus  obtained,  estimated  after  the  usual 
manner,  gave  means  for  calculating  the  atomic  weight  of  chromium. 
His  figures,  reduced  to  a  common  standard,  give,  as  proportional  to  100 
parts  of  chloride  of  silver,  the  quantities  of  chromic  chloride  stated  in 
the  third  of  the  subjoined  columns  : 

.2367  grm.  CrCls  gave  .6396  grm.  AgCl.  37-Oo; 

.2946  "  .7994  36.853 

.2593  -7039  36-838 

.4935  I-3395  36.842 

.5850  "              1.5884  "                       36-830 

.6511  "              1.76681  "                       36.852 

.5503  "              L4939I  "                       36.836 

Mean,  36.865,  ±  .0158 

The  first  of  these  figures  varies  so  widely  from  the  others  that  we  are 
justified  in  rejecting  it,  in  which  case  the  mean  becomes  86.842,  ±  .0031. 

Siewert  also  made  two  analyses  of  silver  dichromate  by  the  following 
process.  The  salt,  dried  at  120°,  was  dissolved  in  nitric  acid.  The  silver 
was  then  thrown  down  by  hydrochloric  acid,  and,  in  the  filtrate,  chro- 
mium hydroxide  was  precipitated  by  ammonia.  Reduced  to  a  uniform 
standard,  we  find  from  his  results,  corresponding  to  100  parts  of  AgCl, 
Ag2O207  as  in  the  last  column : 

.7866  grm.  Ag2Cr2O7  gave  .52202  AgCl  and  .2764  Cr2O3.  150.684 

1.089  "  .72249       "  .3840      "  150.729 

Berlin's  single  determination  of  this  ratio  gave  151.035.  Taking  all 
three  values  together  as  one  series,  they  give  a  mean  of  150.816,  ±  .074. 

Siewert's  percentages  of  Cr.203  obtained  from  Ag2O2Or  are  as  follows, 
calculated  from  the  above  weighings  : 

35-'39 
35.262 

Mean,  35.2005,  ±  .0415 
*  Zeit.  Gesammt.  Wissenschaften,  17,  530. 


244  THE    ATOMIC    WEIGHTS. 

Combining,  as  before,  with  Berlin's  single  result,  giving  the  latter  equal 
weight  with  one  of  these,  we  have  a  general  mean  of  35.236,  ±  .0335. 

For  the  ratio  between  silver  chloride  and  chromic  oxide,  Siewert's  two 
analyses  of  the  dichromate  come  out  as  follows.  For  100  parts  of  AgCl 
we  have  of  Cr208 : 


Mean,  53.049,  ±  .068 

This  figure,  reduced  to  the  standard  of  Berlin's  work  on  the  mono- 
chromate,  becomes  26.525,  ±  .034.  Berlin's  mean  was  26.682,  ±  .0076. 
The  two  means,  combined,  give  a  general  mean  of  26.676,  ±  .074. 

By  Baubigny  *  we  have  only  three  experiments  upon  the  calcination 
of  anhydrous  chromic  sulphate,  as  follows : 

1.989  grm.  Cr2(SO4)8  gave  .7715  grm.  Cr.2O3.  38.788  per  cent. 

3.958  "  1.535  "  38.782      " 

2.6052  1.0115  "  38.826       " 

Mean,  38:799,  ±  .0092 

Moberg  found  for  the  same  ratio  the  percentage  39.195,  ±  .028.  The 
general  mean  of  both  series,  Moberg's  and  Baubigny's,  is  38.838,  ±  .0087. 

In  Rawson's  work  f  ammonium  dichromate  was  the  substance  studied. 
Weighed  quantities  of  this  salt  were  dissolved  in  water,  and  then  reduced 
by  hydrochloric  acid  and  alcohol.  After  evaporation  to  dryness  the  mass 
was  treated  with  water  and  ammonia,  reevaporated,  dried  five  hours  at 
140°,  and  finally  ignited  in  a  muffle.  The  residual  chromic  oxide  was 
bright  green,  and  was  tested  to  verify  its  purity.  The  corrected  weights 
are  as  follows  : 

Am^Cr^O-.  Cr.2Os.                       Percent.  Cr.2O3. 

1.01275  -61134  60.365 

1.08181  .65266  60.330 

1.29430  -78090  60.334 

1.13966  .68799  60.368 

•98778  .59595  60.332 

1.14319  .68987  60.346 


Mean,  60.346,  ±  .0046 

Latest  in  time  and  most  elaborate  of  all,  we  come  to  the  determinations 
of  the  atomic  weight  of  chromium  made  by  Meineke,J  who  studied  the 
chromate  and  ammonio-chromate  of  silver,  and  also  the  dichromates  of 
potassium  and  ammonium.  For  the  latter  salt  he  measured  the  same 
ratio  that  Rawson  determined,  but  by  a  different  method.  He  precipi- 


*Compt.  Rend.,  98,  146. 

tjourn.  Chem.  Soc.,  55,  213. 

t  Ann.  d.  Chem.,  261,  339.     1891. 

• 


CHROMIUM. 


245 


tated  its  solution  with  mercurous  nitrate,  and  ignited  the  precipitate, 
with  the  subjoined  results.    Vacuum  weights  are  given ; 

Am.2Cr.2Or  Cr2Os.  Percent.  Cr2Os. 

2.0416  1.2316  60.325 

2.1618  1.3040  60.320 

2.0823  1.2562  60.328 

2.1913  1.3221*  60.335 

2.0970  1.2656  60.353 


Mean,  60.332,  ±  .0037 
Rawson  found,  60.346,  ±  .0046 


General  mean,  60.337,  =b  .0029 

The  chromate  of  silver,  Ag.2Cr04,  and  the  ammonio-chromate, 
Ag,Cr04.4NH3,  both  prepared  with  all  necessary  precautions  to  insure 
purity,  were  first  treated  essentially  as  in  Berlin's  experiments,  except 
that  the  traces  of  silver  chloride  held  in  solution  by  the  chromic  chloride 
were  thrown  out  by  sulphuretted  hydrogen,  estimated,  and  their  amount 
added  to  the  main  portion.  Thus  the  chief  error  in  Berlin's  work  was 
avoided.  I  subjoin  the  data  obtained,  with  vacuum  standards,  as  usual. 
All  of  Meineke's  results  are  so  corrected : 


Ag.CrO,. 

2.7826 
3.2627 
3.6362 
4.6781 
3-2325 
3-9I37 


AgCL 

2.4047 
2.8199 
3.1416 
4.0414 
2.7930 
3-3805 


.6384 

.7480 

•8338 

1.0726 

-74H 
.8976 


Hence  we  have  the  following  ratios,  as  in  the  case  of  Berlin's  data : 

Percent.  Cr.2Os.  looAgCl :  Ag^CrO^.  looAgCl : 

22.943  "5-7I5  26.548 

22.926  "5.703  26.526 

22.931  115.744  26.602 

22.928  115.754  26.601 

22.924  "5.736  26.531 

22.935  "5-773  26.552 


Mean,  22.931,  ±  .0019 
Berlin,  23.014,  =t  .0110 


Mean,  115.737,  ±  .0072    Mean,  26.560,  ±  .0093 
Berlin,  115.956,  db  .0230 


General  mean,  22.934,  =h  .0018    General  mean,  115.760,  ±  .0069 

With  the  ammonio-chromate  Meineke  found  as  follows : 
'  AgCL  Cr,O,. 


4.1518 
4.2601 
5.9348 


2.9724 
3.0592 
4.2654 


•  79°4 

.8125 

1.1317 


*  Calculated  back  from  Meineke's  value  for  Cr,  to  replace  an  evident  misprint  in  the  original. 


246  THE    ATOMIC    WEIGHTS. 

And  the  ratios  become — 

Percent.  Cr.,O.A.  looAgCl :  Salt.  woAgCl :  Cr.,O3. 
19.037                                139-679  26.591 

19.072  139.255  26.559 

19.059  i39-I38  26.532 

Mean,  19.059,  HZ  .0074    Mean,  139.357,  ±  .1 109    Mean,  26.561,  =h  .01 15 

The  first  of  these  three  analyses  is  rejected  by  Meineke  as  suspicious, 
but  for  the  present  I  shall  allow  it  to  remain.  The  data  in  the  third 
column  may  now  be  combined  with  the  corresponding  figures  from  the 
normal  chromate,  as  found  by  Meineke  and  his  predecessors. 

Berlin 26.682,  ±  .0076 

Siewert,  from  Ag2Cr2O7 26.525,  ±  .0340 

Meineke,  from  Ag2CrO4 26.560,  ±  .0093 

Meineke,  from  Ag2CrO4>4NH3 26.561,  dr  .0115 


General  mean  .....................    26.620,  rb  .0052 

:  Cr2O3  :  :  100  :  26.620,  ±  .0052 


Obviously,  this  mean  is  vitiated  by  the  known  error  in  Berlin's  work, 
the  ultimate  effect  of  which  is  yet  to  be  considered. 

In  all  four  of  the  salts  studied  by  Meineke  he  determined  volumetric- 
ally  the  oxygen  in  excess  of  the  normal  oxides  by  measuring  the  amount 
of  iodine  liberated  in  acid  solutions.  With  the  silver  salts  the  process 
was  essentially  as  follows  :  A  weighed  quantity  of  the  chromate  was  dis- 
solved in  weak  ammonia,  and  the  solution  was  precipitated  with  potas- 
sium iodide.  After  the  silver  iodide  had  been  filtered  off,  five  or  six 
grammes  of  potassium  iodide  were  added  to  the  filtrate,  which  was  then 
acidulated  with  phosphoric  acid  and  a  little  sulphuric.  The  liberated 
iodine  was  then  titrated  with  sodium  thiosulphate  solution,  which  had 
been  standardized  by  means  of  pure  iodine,  prepared  by  Stas'  method, 
From  the  iodine  thus  measured  the  excessive  oxygen  was  computed,  and 
from  that  datum  the  atomic  weight  of  chromium  was  found.  For  pres- 
ent purposes,  however,  the  data  may  be  used  more  directly,  as  giving  the 
ratios  I3  :  Ag2Cr04  and  I,  :  Ag2Cr04.4NH3.  Thus  treated,  the  weights  are 
as  follows,  reduced  to  a  vacuum.  Reckoning  the  salt  as  100,  the  third 
column  gives  the  percentage  of  iodine  liberated  : 

Ag.fr  O±.  I  Set  Free.  Percentage. 

.43838  .50251                               114.628 

.90258  1.03432                              H4-595 

.89858  1.02980                              114.603 

.89868  1.03072  T  14.693 

Mean,  114.630,  ±  .015 


CHROMIUM.  247 

The  next  series,  obviously,  gives  the  ratio  I3 :  Ag2CrO4.4NH3. 

/  Set  Free.  Percentage  * 


.54356  .51784  95-267 

.54856  .52046  94.877 

.54926  .52322  95.258 

.54906  .52376  95.392 

.54466  .5*910  95.307 

.54536  .51891  95- 15° 

Mean,  95.208,  =b  .0497 

In  dealing  with  the  two  dichromates  Meineke  used  the  acid  potassium 
iodate  in  place  of  potassium  iodide,  the  chromate  and  the  iodate  reacting 
in  the  molecular  ratio  of  2:1.  The  thiosulphate  was  standardized  by 
means  of  the  acid  iodate,  so  that  we  have  direct  ratios  between  the  latter 
and  the  two  chromates.  The  data  are  as  follows,  with  the  amount  of 
iodate  proportional  to  one  hundred  parts  of  the  dichromate  in  the  third 
column : 

Percentage. 


.25090 

.16609 

66.198 

.25095 

.16613 

66.200 

.25078 

.16601 

66.197 

.24979 

.16541 

66.220 

.24987 

.16540 

66.192 

.24966 

•16543 

66.262 

.25015 

•16559 

66.196 

.25012 

.16559 

66.204 

.24977 

.16546 

66.245 

.25034 

.16572 

66.198 

.25025 

.16567 

66.202 

.25015 

.16568 

66.234 

Mean,  66.212,  ±  .0044 

Am.2Cr.l0r 

KHI^O, 

Percentage. 

.21457 

.16584 

77.290 

.21465 

.16588 

77.279 

.21464 

.16584 

77-264 

.21416 

.'6543 

77.246 

.21447 

.16564 

77.232 

.21427 

•16559 

77.281 

.22196 

.17152 

77.272 

.22194 

•17151 

77.278 

.22180 

•'7139 

77-272 

Mean,  77.268,  ±  .0041 

*  These  figures  are  not  wholly  in  accord  with  the  percentages  of  oxygen  computed  by  Meineke. 
I  suspect  that  there  is  a  misprint  among  his  data  as  published,  probably  in  the  second  experi- 
ment, but  I  cannot  trace  it  with  certainty. 


248  THE    ATOMIC    WEIGHTS. 

The  following  ratios  are  now  available  for  computing  the  atomic  weight 
of  chromium  : 

(i.)   Percentage  Cr2O3  from  Ag2CrO4,  22.934,  ±  .0018 
(2.)   Percentage  Cr2O3  from  Ag2Cr2O7,  35.236,  =b  .0335 
(3.)  2AgCl  :  Ag2CrO4  :  :  loo  :  115.760,  rb  .0069 
(4.)  2AgCl  :  Ag2Cr2O7  :  :  100  :  150.816,  ±  .074 
(5.)  4AgCl  :  Cr2O3  :  :  loo  :  26.620,  rb  .0052 
(6.)   Percentage  Cr2O3  in  Cr2(SO4)3,  38.838,  =b  .0087 
(7.)   Percentage  Cr2O3  in  AmCr(SO4)2.  12H2O,  16.143,  ±  .0125 
(8.)   BaSO4  :  BaCrO4  :  :  100  :  108.9815,  ±  .0369 
/        (9.)   BaCrO4  :  BaCl2  :  :  100  :  81.702,  ±  .014 
(10.)  3AgCl  :  CrCl3  :  :  100  :  36.842,  ±  .0031 
(II.)   2KC1O3  :  K2Cr2O7  :  :  100  :  120.216,  rb  .0235 
(12.)   Percentage  Cr2O3  in  Ag2CrO4.4NH3,  19.059,  ±  .0074 
(13  )  2AgCl  :  Ag2CrO4.4NH3  :  :  100  :  139.357,  d=  .1109 
(14.)   Percentage  Cr2O3  in  Am2Cr2O7,  60.337,  ±  .0029 
(15.)   Ag2CrO4  :  3!  :  :  100  :  114.630,  ±  .015 
(16.)  Ag2CrO4.4NH3  :  3!  :  :  100  :  95.208,  ±  -O497 
(17.)  2K2Cr2O7  :  KHI2O6  :  :  100  :  66.212,  =b  .0044 
(18.)   2Am2Cr2O7  :  KHI2O6  :  :  100  :  77.268,  ±  .0041 

The  antecedent  values  to  use  in  the  reduction  are  — 

0  =  15  879,  ±  .0003  S     =  31.828,  rb  .0015 
Ag  =  107.  108,  zb  .0031  N   =  13.935,  rb  .0021 
Cl  =  35.179,  rb  .0048  Ba   —  136.392,  rb  .0086 

1  =  125.888,  rb  .0069  AgCl  =  142.287,  ±  .0037 
K  =  38.817,  ±  .0051 

For  the  molecular  weight  of  CraOs,  seven  values  are  now  calculable,  as 
follows  : 

From  (i)  ................  ......  Cr2O3  —  151.120,  ±  .0130 

From  (2)  ......................  "  =  151.105,  rb  .1636 

From  (5)  ......................  "  =  151.507,  ±  .0299 

From  (6)  ..................  ----  "  =  151.384,^.0341 

Prom  (7)  .....................  "  =.-  153.756,  ±.1205 

From  (12)  .....................  "  —  151.478,  ±  .0606 

From  (14)  .....................  "  =•  151.190,  ±  .0110 

General  mean  ............    Cr2O3  =  151.229,  ±  .0039 

For  silver  chromate  there  are  two  values— 

From  (3)  ....................   Ag2CrO4  =  329.423,  ±  .0195 

From  (15)  ...................          "         =r  329.464,  it  .0467 

General  mean  ..........   Ag2CrO4  =  329.430,  rb  .0180 

And  for  the  ammonio-chromate  we  have  — 


From  (13)  .............   Ag2CrO4.4NH3  =  396-574,  ±  - 

From  (16)  .............  "  =  396.673,  rb  .2082 


General  mean Ag.2CrO4.4NH3  =  396.647,  ±  .1738 


CHROMIUM.  249 

From  (4) Ag2Cr2O7   =  429-177,  ±  .2109 

From  (10) CrCl3          =  157.266,  dr  .01 13 

From  (18) Am2Cr2O7  —  250.341,  dr  .0164 

For  the  molecular  weights  of  K2Cr207  and  BaCr04  there  are  two  esti- 
mates each,  as  given  below : 

From  (u) K2Cr2O7  =  292.433,  =b  .0189 

From  (17) "         =  292.143,  =b  .0224 


General  mean K2Cr2O7  =  292.311,  dr  .0144 

From  (8) BaCrO4  =  252.549, ,dr  .0966 

From  (9) "        =  253.054,  ±  .0377 

General  mean BaCrO4  —  252.985,  ±  .0351 

Finally,  from  these  molecular  weights,  eight  independent  values  are 
obtained  for  the  atomic  weight  of  chromium  : 

From  Cr2O3 Cr  =  5 1 . 796,  dr  .0039 

From  Ag2CrO4 "  ===  51.698,  dr  .0191 

From  Ag2CrO4,  4NH3 "  =51.175,  ±.1741 

From  Ag2Cr2O7 "  =  51.904,  dr  .1055 

From  Am2Cr2O7 "  —  51.659,  ±  .0085 

From  K2Cr2O7 "=  51.762,  ±  .0102 

From  CrCl3 "  =51.729,  dr  .0183 

From  BaCrO4 "  =  53.077,  ±  .0362 

General  mean Cr  =  51.778,  dr  -0032 

If  0  =  16,  Cr  =  52.172. 

Rejecting  the  last  of  the  eight  values,  that  from  barium  chromate,  the 
mean  becomes — 

Cr  =  51. 767,  ±.0032. 

Even  this  result  is  probably  too  high,  for  it  includes  ratios  which  are 
certainly  erroneous,  and  which  yet  exert  appreciable  weight.  From  the 
ratios  which  are  reasonably  concordant  a  better  mean  is  derivable,  as 
follows : 

From  (l) Cr  —  51.741,  dr  .0065 

From  (2).. "  =51.734,  db  .0818 

From  (14) "  =51.776,  ±  .0055 

From  (3)  and  (15) "  =  51.698,  d=  .0191 

From  (4) "  =51.904,  ±  .1055 

From  (10) "  =  51.729,  dr  .0183 

From  (18) <c  =  51.659,  ±  .0085 

From  (i  i)  and  (17) '«  =.  51.762,  dr  .0102 


General  mean Cr  =  51.742,  dr  .0034 

If  0  =  16,  this  becomes  52.136,  a  value  which  is  probabty  not  very 
far  from  the  truth. 


250  THE   ATOMIC   WEIGHTS. 


MOLYBDENUM. 

If  we  leave  out  of  account  the  inaccurate  determination  made  by 
Berzelius,*  we  shall  find  that  the  data  for  the  atomic  weight  of  molyb- 
denum lead  to  two  independent  estimates  of  its  value — one  near  92,  the 
other  near  96.  The  earlier  results  found  by  Berlin  and  by  Svanberg  and 
Struve  lead  to  the  lower  number;  the  more  recent  investigations,  to- 
gether with  considerations  based  upon  the  periodic  law,  point  conclu- 
sively to  the  higher. 

The  earliest  investigation  which  we  need  especially  to  consider  is  that 
of  Svanberg  and  Struve.  f  These  chemists  tried  a  variety  of  different 
methods,  but  finally  based  their  conclusions  upon  the  two  following : 
First,  molybdenum  trioxide  was  fused  with  potassium  carbonate,  and 
the  carbon  dioxide  which  was  expelled  was  estimated  ;  secondly,  molyb- 
denum disulphide  was  converted  into  the  trioxide  by  roasting,  and  the 
ratio  between  the  weights  of  the  two  substances  was  determined. 

By  the  first  method  it  was  found  that  100  parts  of  MoO3  will  expel  the 
following  quantities  of  C02 : 

3L4954 
3  * -3749 
31-4705 

Mean,  31.4469,  ±  .0248 

The  carbon  dioxide  was  determined  simply  from  the  loss  of  weight 
when  the  weighed  quantities  of  trioxide  and  carbonate  were  fused  to- 
gether. It  is  plain  that  if,  under  these  circumstances,  a  little  of  the 
trioxide  should  be  volatilized,  the  total  loss  of  weight  would  be  slightly 
increased.  A  constant  error  of  this  kind  would  tend  to  bring  out  the 
atomic  weight  of  molybdenum  too  low. 

By  the  second  method,  the  conversion  by  roasting  of  MoS2  into  Mo03, 
Svanberg  and  Struve  obtained  these  results.  Two  samples  of  artificial 
disulphide  were  taken,  A  and  B,  and  yielded  for  each  hundred  parts  the 
following  of  trioxide : 

89-79191  A 
89.7291  / 

89.6436] 
89.7082  I 
89.7660  j-B. 
-  89.7640  | 
89-8635] 


Mean,  89.7523,  ±  .0176 


Three  other  experiments  in  series  B  gave  divergent  results,  and,  al- 
though published,  are  rejected  by  the  authors  themselves.     Hence  it  is 


*  Poggend.  Annalen,  8,  i.     1826. 

t  Journ.  fur  Prakt.  Chem.,  44,  301.     1848. 


MOLYBDENUM. 


251 


not  necessary  to  cite  them  in  this  discussion.  We  again  encounter  in 
these  figures  the  same  source  of  constant  error  which  apparently  vitiates 
the  preceding  series,  namely,  the  possible  volatilization  of  the  trioxide. 
Here,  also-,  such  an  error  would  tend  to  reduce  the  atomic  weight  of 
molybdenum. 

From  the  CO2  series Mo  —  91.25 


From  the  MoS.,  series. 


Mo  =  92.49 


Berlin,*  a  little  later  than  Svanberg  and  Struve,  determined  the  atomic 
weight  of  molybdenum  by  igniting  a  molybdate  of  ammonium  and 
weighing  the  residual  MoO3.  Here,  again,  a  loss  of  the  latter  by  vola- 
tilization may  (and  probably  does)  lead  to  too  low  a  result.  The  salt 
used  was  (Nll4)4MoftOtt.BH,O,  and  in  it  these  percentages  of  Mo03  were 
found  : 

81.598 

81.612 

81.558 

81-555 


Mean,  81.581,  ±  .0095 

Hence  Mo  =  91.559. 

Until  1859  the  value  92  was  generally  accepted  on  the  basis  of  the  fore- 
going researches,  but  in  this  year  Dumas  f  published  some  figures  tend- 
ing to  sustain  a  higher  number.  He.  prepared  molybdenum  trioxide 
by  roasting  the  disulphide,  and  then  reduced  it  to  metal  by  ignition  in 
hydrogen.  At  the  beginning  the  hydrogen  was  allowed  to  act  at  a  com- 
paratively low  temperature,  in  order  to  avoid  volatilization  of  trioxide; 
but  at  the  end  of  the  operation  the  heat  was  raised  sufficiently  to  insure 
a  complete  reduction.  From  the  weighings  I  calculate  the  percentages 
of  metal  in  MoO3 : 


.448  grm.  MoO3  gave  .299  grm.  Mo. 
.484  "  .323 

.484  .322 

.498  .332 

•559  "  -373 

.388  "  .258 


66.741  per  cent, 
66.736  " 
66.529  " 
66.667  " 
66.726  " 
66.495  " 


Mean,  66.649,  ±  •°3° 


In  1868  the  same  method  was  employed  by  Debray.J  His  trioxide 
was  purified  by  sublimation  in  a  platinum  tube.  His  percentages  are 
as  follows : 


5.514  grm.  MoO3  gave  3.667  grm.  Mo. 
7.910  "  5.265 

9.031  "  6.015          " 


66.503  per  cent. 
61.561 
66.604        " 


Mean,  66.556,  =b  .020 


*  Journ.  fur  Prakt.  Chem.,  49,  444.     1850. 
f  Ann.  Chem.  Pharm.,  105,  84,  and  113,  23. 
J  Compt.  Rend.,  66,  734. 


252  THE    ATOMIC    WEIGHTS. 

For  the  same  ratio  we  have  also  a  single  experiment  by  Rammelsberg,* 
who,  closely  following  Dumas'  method,  found  in  molybdenum  trioxide 
66.708  per  cent,  of  metal.  As  this  figure  falls  within  the  limits  of  Dumas' 
series,  we  may  assign  it  equal  weight  with  one  experiment  in  the  latter. 

Debray  also  made  two  experiments  upon  the  precipitation  of  molyb- 
denum trioxide  in  ammoniacal  solution  by  nitrate  of  silver.  In  his  re- 
sults, as  published,  there  is  curious  discrepancy,  which,  I  have  no  doubt, 
is  due  to  a  typographical  error.  These  results  I  am  therefore  compelled 
to  leave  out  of  consideration.  They  could  not,  however,  exert  a  very 
profound  influence  upon  the  final  discussion. 

In  1873,  Lothar  Meyer  f  discussed  the  analyses  made  by  Liechti  and 
Kemp  J  of  four  chlorides  of  molybdenum,  and  in  the  former  edition  of 
this  work  the  same  data  were  considered  in  detail.  The  analyses,  how- 
ever, were  not  intended  as  determinations  of  atomic  weight,  and  since 
good  determinations  have  been  more  recently  published,  the  work  on 
the  chlorides  will  be  omitted  from  further  consideration.  It  is  enough 
to  state  here  that  they  gave  values  for  Mo  ranging  near  96,  both  above 
and  below  that  number,  with  an  extreme  range  of  over  eight-tenths  of  a 
unit. 

In  1893  the  determinations  by  Smith  and  Maas  appeared,  §  represent- 
ing an  entirely  new  method.  Sodium  molybdate,  purified  by  many  re- 
crystallizations  and  afterwards  dehydrated,  was  heated  in  a  current  of 
pure,  dry,  gaseous  hydrochloric  acid.  The  compound  MoO3.2HCl  was 
thus  distilled  off,  and  the  sodium  molybdate  was  quantitatively  trans- 
formed into  sodium  chloride.  The  latter  salt  was  afterwards  carefully 
examined,  and  proved  to  be  free  from  molybdenum.  The  data,  with  all 
weights  reduced  to  a  vacuum  standard,  are  subjoined  : 


NaCl.  Per  cent.  NaCL 

1.14726  .65087  56.733 

.89920  .5I023  56-743 

.70534  .40020  56.739 

•7°793  .40182  56.760 

1.26347  .71695  56.745 

1.15217  .65367  56.734 

.90199  .51188  5675° 

.81692  .46358  .    56.747 

.65098  .36942  56.748 

.80563  .45717  56.747 

Mean,  56.745,  ±  .0017 

In  1895,  Seubert  and  Pollard  ||  determined  the  atomic  weight  of  mo- 

*  Berlin  Monatsbericht,  1877,  p.  574- 
f  Ann.  Chem.  Pharm.,  169,  365.     1873. 
I  Ann.  Chem.  Pharm.,  169,  344. 
\  Journ.  Amer.  Chem.  Soc.,  15,  397.     1893. 
||  Zeitsch.  Anorg.  Chem.,  8,  434.     1895. 


MOLYBDENUM.  253 

lybdenum  by  two  methods.  First,  the  carefully  purified  trioxide,  in 
weighed  amounts,  was  dissolved  in  an  excess  of  a  standard  solution  of 
caustic  soda.  This  solution  was  standardized  by  means  of  hydrochloric 
acid,  which  in  turn  had  been  standardized  gravimetrically  as  silver 
chloride.  Hence,  indirectly,  the  ratio  2AgCl  :  Mo03  was  measured.  Sul- 
phuric acid  and  lime  water  were  also  used  in  the  titrations,  so  that  the 
entire  process  was  rather  complicated.  Ignoring  the  intermediate  data, 
the  end  results,  in  weights  of  MoO3  and  AgCl,  were  as  follows.  The  third 
column  gives  the  Mo03  proportional  to  100  parts  of  AgCl  : 


MoO3.  AgCl.  Ratio. 

3.6002  7.!7°9  50.206 

3.5925  7.i569  50-196 

3-73"  7.4304  50-214 

3.8668  7.7011  50.211 

3.9361  7-8407  50.201 

3.8986  7.7649  50.208 

3.9630  7.8941  50.202 

3-9554  7.8806  50.  192 

3.9147  7-7999  5°.  i§9 

3.8543  7.6767  50.208 

3.9367  7.8437  50-190 


Mean,  50.202,  ±  .0018 

The  second  method  adopted  by  Seubert  and  Pollard  was  the  old  one 
of  reducing  the  trioxide  to  metal  by  heating  in  a  current  of  hydrogen. 
The  weights  and  percentages  of  metal  are  subjoined  : 


Mo.  Per  rent. 
1.8033                                i.  2021  66.661 

1.9345  1.1564  66.670 

3.9413  2.6275  66.666 

1.5241  i.  0160  66.662 

4.0533  2.7027  66.679 


Mean,  66.668,  ±  .0022 

This  mean  may  be  combined  with"  the  results  of  previous  investigators, 
thus : 

Dumas 66.649,  ±  .0300 

Debray 66.556,  ±  .0200 

Rammelsberg 66.708,  db  .0680 

Seubert  and  Pollard. 66.668,  ±  .0022 

General  mean 66.665,  ±   0022 

Here  the  data  of  Seubert  and  Pollard  alone  exert  any  appreciable 
influence. 

Neglecting  all  determinations  made  previous  to  1859,  there  are  now 


254  THE    ATOMIC    WEIGHTS. 

three  ratios  from  which  to  compute  the  atomic  weight  of  molybdenum, 

viz  : 

(i.)   Percentage  Mo  in  MoO3,  66.665,  =b  .0022. 
(2.)   2AgCl  :  MoO3  :  :  100  :  50.202,  ±  .0018 
(3.)   2NaCl  :  Ma.2MoO4  :     56.745,  ±  .0017  :  100. 

These  involve  the  following  values  : 

O   =  15.879,  ±  .0003  AgCl  —  142.287,  ±  .0037 

Na  =  22.881,  ±.0046  NaCl  =    58.060,^.0017 


Hence  for  the  atomic  weight  in  question  — 

From  (i)  .........................    Mo  =  95.267,  ±  .0072 

From  (2)  .........................     "   =  95.225,  ±  .0064 

From  (3)  ........................     "   —95.357,  ±  .0126 

General  mean  ...............    Mo  =  95.259,  ±  .0045 

With  0  =  16,  Mo  =  95.985. 

This  value  is  essentially  that  derived  from  Seubert  and  Pollard's  data 
alone.  Reducing  the  latter  to  a  vacuum  would  affect  the  result  very 
slightly  —  so  slightly  that  the  correction  may  be  ignored. 


TUNGSTEN.  255 


TUNGSTEN. 

The  atomic  weight  of  tungsten  has  been  determined  from  analyses  or 
the  trioxide,  the  hexchloride,  and  the  tungstates  of  iron,  silver,  and 
barium. 

The  composition  of  the  trioxide  has  been  the  subject  of  many  investi- 
gations. Malaguti  *  reduced  this  substance  to  the  blue  oxide,  and  from 
the  difference  between  the  weights  of  the  two  compounds  obtained  a 
result  now  known  to  be  considerably  too  high.  In  general,  However, 
the  method  of  investigation  has  been  to  reduce  W03  to  W  in  a  stream 
of  hydrogen  at  a  white  heat,  and  afterwards  to  reoxidize  the  metal,  thus 
getting  from  one  sample  of  material  two  results  for  the  percentage  of 
tungsten.  This  method  is  probably  accurate,  provided  that  the  trioxide 
used  be  pure. 

The  first  experiments  which  we  need  consider  are,  as  usual,  those  of 
Berzelius.f  899  parts  WO3  gave,  on  reduction,  716  of  metal.  676  of 
metal,  reoxidized,  gave  846  W03.  Hence  these  percentages  of  W  in 
W03: 

79.644,  by  reduction. 
79.905,  by  oxidation. 

Mean,  79.7745,  ±  .0880 

These  figures  are  far  too  high,  the  error  being  undoubtedly  due  to  the 
presence  of  alkaline  impurity  in  the  trioxide  employed. 

Next  in  order  of  time  comes  the  work  of  Schneider,  J  who  with  char- 
acteristic carefulness,  took  every  precaution  to  get  pure  material.  His 
percentages  of  tungsten  are  as  follows : 

Reduction  Series. 

79.336 
79-254 
79.312 
79.326 
79-350 


Mean,  79.3156 
Oxidation  Series. 


79324 
79.328 


Mean,  79-327 
Mean  of  all,  79.320,  =b  .0068 


*  Journ.  fiir  Prakt.  Chem.,  8,  179.     1836. 

fPoggend.  Aiinalen,  8,  i.     1826. 

J Journ.  fiir  Prakt.  Chem.,  50,  152.     1850. 


256  THE    ATOMIC    WEIGHTS. 

Closely  agreeing  with  these  figures  are  those  of  Marchand,*  published 
in  the  following  year  : 

Reduction  Series. 

79.307 
79.302 


Mean,  79.3045 

Oxidation  Series. 
79.321 
79.352 


Mean,  79.3365 
Mean  of  all,  79.3205,  =b  .0073 

The  figures  obtained  by  v.  Borch  f  agree  in  mean  tolerably  well  with 
the  foregoing.     They  are  as  follows  : 

Reduction  Series. 
79.310 
79.212 
79.289 

79.313 
79.225 

79-290 
79.302 


Mean,  79-277 
Oxidation  Series. 

79-359 
79-339 


Mean,  79.349 
Mean  of  all,  79.293,  ±  .0108 

Dumas  J  gives  only  a  reduction  series,  based  upon  trioxide  obtained 
by  the  ignition  of  a  pure  ammonium  tungstate.  The  reduction  was 
effected  in  a  porcelain  boat,  platinum  being  objectionable  on  account  of 
the  tendency  of  tungsten  to  alloy  with  it.  Dumas  publishes  only 
weighings,  from  which  I  have  calculated  the  percentages : 


2.784  grm. 

WO3  gave  2.208  grm.  \V 

7Q.  's  IO 

per  cent. 

2,994 

2.373       " 

79.259 

" 

4.600 

3.649       " 

79.326 

11 

.985 

.781 

79.289 

11 

.917 

.727       " 

79.280 

" 

.917 

.728       " 

79-389 

" 

1.717 

1.362       " 

79-324 

" 

2.988 

2.370       " 

79-3*7 

" 

Mean,  79.312, 

±  .009 

*  Ann.  Cheni.  Pharni.,  77,  261.     1851. 

t  Journ.  fur  Prakt.  Chem.,  54,  254.     1851. 

JAnn.  Chem.  Pharni. ,  113,  23.     1860. 


TUNGSTEN.  257 

The  data  furnished  by  Bernoulli*  differ  widely  from  those  just  given. 
This  chemist  undoubtedly  worked  with  impure  material,  the  trioxide 
having  a  greenish  tinge.  Hence  the  results  are  too  high.  These  are  the 
percentages  of  W  : 

Reduction  Series. 

79.556 
79.526 

79-553 
79.558 
79-549 
78.736 


Mean,  79.413 

Oxidation  Series. 

79.55« 
79.656. 

79-555 
79-554 


Mean,  79.581 
Mean  of  all,  79.480,  ±  .056 

Two  reduction  experiments  by  Persozf  give  the  following  results  : 

1-7999  Srm-  WO3  gave  1.4274  grm-  w-  79-3°4  per  cent. 

2.249  "  1-784         "  79.324       " 

Mean,  79.314,  ±  .007 

Next  in  order  is  the  work  done  by  Roscoe.  J  This  chemist  used  a 
porcelain  boat  and  tube,  and  made  six  weighings,  after  successive  reduc- 
tions and  oxidations,  with  the  same  sample  of  7.884  grammes  of  trioxide. 
These  weighings  give  me  the  following  five  percentages,  which,*for  the 
sake  of  uniformity  with  foregoing  series,  I  have  classified  under  the 
usual,  separate  headings  : 

Reduction  Series. 


Mean,  79.263 

Oxidation  Series. 
79.230 
79  299 


Mean,  79.2645 
Mean  of  all,  79.264,  ±  .0146 


*Poggend.  Annalen,  in,  573.     1860. 
t  Zeit.  Anal.  Chem.,  3,  260.     1864. 
\  Ann.  Chem.  Pharm.,  162,368.     1872. 

17 


258  THE    ATOMIC    WEIGHTS. 

In  Wadd  ell's  experiments*  especial  precautions  were  taken  to  pro- 
cure tungstic  oxide  free  from  silica  and  molybdenum.  Such  oxide, 
elaborately  purified,  was  reduced  in  hydrogen,  with  the  following  results : 

1.4006  grm.  WO3  gave  1.1115  W.  79-359  per  cent. 

.9900      "      .7855  "  79-343   " 

1.1479  -9"°  "  79-362   " 

.9894  .7847  "  79-311 

4.5639  3.6201  "  79.320   " 

79-339,  ±.0069 

The  investigation  by  Pennington  and  Smith  f  started  from  the  sup- 
position that  the  tungsten  compounds  studied  by  their  predecessors  had 
not  been  completely  freed  from  molybdenum.  Accordingly,  tungstic 
oxide,  carefully  freed  from  all  other  impurities,  was  heated  in  a  stream 
of  gaseous  hydrochloric  acid,  so  as  to  volatilize  all  molybdenum  as  the 
compound  Mo03.2HCl.  The  residual  WO3,  was  then  reduced  in  pure 
hydrogen,  and  the  tungsten  so  obtained  was  oxidized  in  porcelain 
crucibles.  Care  was  taken  to  exclude  reducing  gases,  and  the  trioxide 
was  finally  cooled  in  vacuum  desiccators  over  sulphuric  acid.  The  oxida- 
tion data  are  as  follows,  with  the  usual  percentage  column  added.  The 
weights  are  reduced  to  a  vacuum : 

Tungsten.   .  Oxygen  Gained.  Percentage. 

.862871  .223952  79-394 

.650700  .168900  79.392 

.597654  .155*43  79-390 

.666820  .173103  79.391 

.428228  .111168  79.390 

.671920  .174406  79.392 

-590220  .153193  79-394 

.568654  .147588  79-394 

1.080973  .280600  79.392 

Mean,  79.392,  dr  .0004 

With  O  =  16,  this  series  gives  W  =  184.92. 

The  very  high  value  for  tungsten  found  by  Pennington  and  Smith, 
nearly  a  unit  higher  than  that  which  was  commonly  accepted,  seems  to 
have  at  once  attracted  the  attention  of  Schneider,^  who  criticised  the 
paper  somewhat  fully,  and  gave  some  new  determinations  of  his  own. 
The  tungsten  trioxide  employed  in  this  new  investigation  was  heated  in 
gaseous  hydrochloric  acid,  and  the  absence  of  molybdenum  was  proved. 
The  data  obtained,  both  by  reduction  and  by  oxidation,  are  as  follows: 

*Am.  Chem.  Journ.,  8,  280.     1886. 

tRead  before  the  Amer.  Philos.  Soc.,  Nov.  2,  1894. 

J  Jourii.  fur  Prakt.  Chem.  (2),  53,  288.     1896. 


TUNGSTEN. 


259 


Reduction  Series. 
2.0738  grm.  WO3  gave  1.6450  W. 
4.0853  "  3-2400  " 

6.1547  "  4.8811   " 


79-323  Per 

79.309 

79.307 


Oxidation  Series. 

1.5253  grm.  W  gave  1.9232  WO3.  79-311  Per  cent. 

3.1938  "  4-0273     "  79.304       " 

4.7468  "  5.9848     "  79.314       » 


Mean  of  all,  79.311,  ±  .0018 

Hence  with  O  =  16,  W  =  184.007. 

In  order  to  account  for  the  difference  between  this  result  and  that  of 
Pennington  and  Smith,  an  impurity  of  molybdenum  trioxide  amounting 
to  about  one  per  cent,  would  be  necessary.  Schneider  suggests  that  the 
quantities  of  material  used  by  Pennington  and  Smith  were  too  small,  and 
that  there  may  have  been  mechanical  loss  of  small  particles  during  the 
long  heatings.  Such  losses  would  tend  to  raise  the  atomic  weight  com- 
puted from  the  experiments.  On  the  other  hand,  the  losses  could  hardly 
have  been  uniform  in  extent,  and  the  extremely  low  prooable  error  of 
Pennington  and  Smith's  series  renders  Schneider's  supposition  improb- 
able. The  error,  if  error  exists,  must  be  accounted  for  otherwise. 

Since  Schneider's  paper  appeared,  another  set  of  determinations  by 
Shinn  *  has  been  published  frond  Smith's  laboratory.  Attempts  to  verify 
the  results  obtained  by  Smith  and  Desi  having  proved  abortive,  and  other 
experiments  having  failed,  Shinn  resorted  to  the  oxidation  method  and 
gives  the  subjoined  data.  The  percentage  column  is  added  by  myself: 

J 


.22297  grm.  W  gave  .28090  \VO3. 
.17200  "  .21664    " 

.10989  " 

.10005  " 


79-377 
79-394 
79-377 
79-417 

Mean,  79.391,  ±  *oo66 

This  figure  is  very  close  to  that  found  in  Pennington  and  Smith's  series, 
and  therefore  serves  as  a  confirmation.  The  discordance  between  these 
results  and  Schneider's  is  still  to  be  explained. 

There  are  still  other  experiments  by  Riche,f  which  I  have  not  been 
able  to  get  in  detail.  They  cannot  be  of  any  value,  however,  for  they 
give  to  tungsten  an  atomic  weight  of  about  ten  units  too  low.  We  may 
therefore  neglect  this  series,  and  go  on  to  combine  the  others  : 

Berzelius 79-7745,  ±  .0880 

Schneider,  1850    79-32O,    ±  .0068 

Marchand 79. 3205,  zfc  .0073 

v.  Borch 79-293,    rb  .oio8 

Dumas 79.3 12,    dz  .0090 


*  Doctoral  thesis.,  University  of  Pennsylvania,  1896.     "  The  atomic  mass  of  tungsten." 
t  Journ.  fur  Prakt.  Chem.,  69,  10.     1857. 


260  THE    ATOMIC    WEIGHTS. 

Bernoulli 79.480,  db  .0560 

Persoz 79-314,  ±  .0070 

Roscoe 79.264,  ±  .0146 

Waddell 79-339,  db  .0069 

Pennington  and  Smith 79. 392,  ±  .0004 

Schneider,  1896 79-31  r,  ±  .0018 

Shinn 79. 39 1 ,  ±  .0066 


General  mean 79-388,    db  .00039 

Here  the  work  of  Pennington  and  Smith  vastly  outweighs  everything 
else;  and  if  their  supposition  as  to  the  presence  of  molybdenum  in  all 
the  previous  investigations  is  correct,  this  result  is  to  be  accepted. 

The  rejection  of  the  figures  given  by  Berzelius  and  by  Bernoulli  would 
exert  an  unimportant  influence  upon  the  final  result.  There  is,  there- 
fore, no  practical  objection  to  retaining  them  in  the  discussion. 

In  1861  Scheibler*  deduced  the  atomic  weight  of  tungsten  from 
analyses  of  barium  metatungstate,  Ba0.4W03.9H20.  In  four  experi- 
ments he  estimated  the  barium  as  sulphate,  getting  closely  concordant 
results,  which  were,  however,  very  far  too  low.  These,  therefore,  are  re- 
jected. But  from  the  percentage  of  water  in  the  salt  a  better  result  was 
attained.  The  percentages  of  water  are  as  follows  : 

13-053 
13-054 
13-045 
13.010 
13.022 


Mean,  13.0368,  ±  .0060 

The  work  of  Zettnow,t  published  in  1867,  was  somewhat  more  com- 
plicated than  any  of  the  foregoing  researches.  He  prepared  the  pure 
tungstates  of  silver  and  of  iron,  and  from  their  composition  determined 
the  atomic  weight  of  tungsten. 

In  the  case  of  the  iron  salt  the  method  of  working  was  this  :  The 
pure,  artificial  FeW04  was  fused  with  sodium  carbonate,  the  resulting 
sodium  tungstate  was  extracted  by  water,  and  the  thoroughly  washed, 
residual  ferric  oxide  was  dissolved  in  hydrochloric  acid.  This  solution 
was  then  reduced  by  zinc,  and  titrated  for  iron  with  potassium  perman- 
ganate. Corrections  were  applied  for  the  drop  in  excess  of  perman- 
ganate needed  to  produce  distinct  reddening,  and  for  the  iron  contained 
in  the  zinc.  11.956  grammes  of  the  latter  metal  contained  iron  corre- 
sponding to  0.6  cc.  of  the  standard  solution.  The  permanganate  was 
standardized  by  comparison  with  pure  ammonium-ferrous  sulphate, 
Am2Fe(S04)2.6H2O,  so  that,  in  point  of  fact,  Zettnow  establishes  directly 
only  the  ratio  between  that  salt  and  the  ferrous  tungstate.  From  Zett 
now's  four  experiments  in  standardizing  I  find  that  1  cc.  of  his  solution 

*  Journ.  fur  Prakt.  Chem.,  83,  324. 
t  Poggend.  Annalen,  130,  30. 


TUNGSTEN.  261 

•corresponds  to  0.0365457  gramme  of  the  double  sulphate,  with  a  prob- 
lable  error  of  ±  .0000012. 

Three  sets  of  titrations  were  made.  In  the  first  a  quantity  of  ferrous 
tungstate  was  treated  according  to  the  process  given  above ;  the  iron 
isolation  was  diluted  to  500  cc.,  and  four  titrations  made  upon  100  cc.  at 
la  time.  The  second  set  was  like  the  first,  except  that  three  titrations 
[were  made  with  100  cc.  each,  and  a  fourth  upon  150  cc.  In  the  third 
(set  the  iron  solution  was  diluted  to  300  cc.,  and  only  two  titrations  upon 
llOO  cc.  each  were  made.  In  sets  one  and  two  thirty  grammes  of  zinc 
[were  used  for  the  reduction  of  each,  while  in  number  three  but  twenty 
grammes  were  taken.  Zettnow's  figures,  as  given  by  him,  are  quite  com- 
plicated ;  therefore  I  have  reduced  them  to  a  common  standard.  After 
applying  all  corrections  the  following  quantities  of  tungstate,  in  grammes, 
correspond  to  1  cc.  of  permanganate  solution  : 


.028301  1 
.028291 
.028311 
.028301  j 
.028367 


First  set. 


Second  set. 

.028367 

.028367  _, 

.028438  I 
.028438  J 

Mean,  .0283549,  ±  .0000115 

With  the  silver  tungstate,  Ag2W04,  Zettnow  employed  two  methods. 
In  two  experiments  the  substance  was  decomposed  by  nitric  acid,  and 
the  silver  thus  taken  into  solution  was  titrated  with  standard  sodium 
chloride.  In  three  others  the  tungstate  was  treated  directly  with  com- 
mon salt,  and  the  residual  silver  chloride  collected  and  weighed.  Here 
again,  on  account  of  some  complexity  in  Zettnow's  figures,  I  am  com- 
pelled to  reduce  his  data  to  a  common  standard.  To  100  parts  of  AgCl 
the  following  quantities  of  Ag2WO4  correspond  : 

By  First  Method. 
161.665 
161.603 


Mean,  161.634,  ±.021 

By  Second  Method. 
161.687 
161.651 
161.613 


Mean,  161.650,  ±  .014 
General  mean  from  both  series,  161.645,  ±  .012 


262 


THE    ATOMIC    WEIGHTS. 


For  tungsten  hexchloride  we  have  two  analyses  by  Roscoe,  published 
in  the  same  paper  with  his  results  upon  the  trioxide.  In  one  experi- 
ment the  chlorine  was  determined  as  AgCl ;  in  the  other  the  chloride 
was  reduced  by  hydrogen,  and  the  residual  tungsten  estimated.  By 
bringing  both  results  into  one  form  of  expression  we  have  for  the  per- 
centage of  chlorine  in  WC16 :  * 

53.588 
53-632 


Mean,  53.610,  d=  .015 

The  work  done  by  Smith  and  Desif  probably  ought  to  be  considered 
in  connection  with  that  of  Pennington  and  Smith  on  the  trioxide. 
Smith  and  Desi  started  with  tungsten  trioxide,  freed  from  molybdenum 
by  means  of  gaseous  hydrochloric  acid.  This  material  was  reduced  in 
a  stream  of  carefully  purified  hydrogen,  and  the  water  formed  was  col- 
lected in  a  calcium  chloride  tube  and  weighed.  To  the  results  found  I 
add  the  percentage  of  water  obtained  from  100  parts  of  WO3.  Vacuum 
weights  are  given. 


WO* 

.983024 

.998424 

i  .008074 

.911974 

•997974 
1.007024 


H.,0. 

.22834 
.23189 
.23409 
.21184 
.23179 
.23389 


Percent. 

23.228 
23.226 
23.221 
23.229 
23.226 
23.226 


Mean,  23.226,  ±  .0008 


There  are  now  six  ratios  from  which  to  calculate  the  atomic  weight  of 
tungsten : 

(I.)   Percentage  of  W  in  WO3,  79.388,  ±  .00039 

(2.)   Percentage  of  H2O  in  BaO.4WO3.9H2O,  13.0368,  db  .0060 

(3.)  WO3  :  3H2O  :  :  100  :  23.226,  db  .0008 

(4.)  Am2Fe(SO4)2.6H2O  :  FeWO4  :  :  .0365457,  d=  .0000012  :  .0283549,  db  .0000115 

(5.)   2AgCl  :  Ag2WO4  :  :  100  :  161.645,  ±  -°12 

(6.)  Percentage  of  Cl  in  WC16,  53.610,  ±  .015 


These  are  reduced  with — 

O  •=  15.879,  d=  .0003 
Ag=  107.108,  dr  .0031 
C1  =  35.179,  ±  .0048 
N  =  13.935,  =b  .0021 


S  =  31.828,  d-  .0015 
Ba  =  136.392,  ±  .0086 
Fe  =  55-597,  ±.0023 
AgCl  =  142.287,  ±  .0037 


*  The  actual  figures  are  as  follows  : 

I9-5700  grm.  WC16  gave  42.4127  grm.  AgCl. 

10.4326  4.8374  grm.  tungsten. 

fRead  before  Amer.  Philos.  Soc.,  Nov.  2,  1894. 


URANIUM.  263 

Hence  there  are  six  values  for  the  atomic  weight  of  tungsten,  as  follows : 

From  (0 W  —  183.485,  ±  .0051 

From  (2) .    "  =  182.638,  ±  .1248 

From  (3) "  =  183  298,  dr  .0088 

From  (4) "  =  183.035,  ±.1229 

From  (5) "  ==  182.268,  db  .0663 

From  (6) "  =  182.647,  ±  .0820 


General  mean W  =  183.429,  ±  .0044 

If  0  =  16,  W  =  184.827.  The  rejection  of  all  values  except  the  first 
and  third  raises  the  mean  by  0.009 ;  that  is,  four  of  the  ratios  count  for 
almost  nothing,  and  the  work  done  in  Smith's  laboratory  dominates  all 
the  rest.  The  questions  raised  by  Schneider  in  his  latest  determination, 
however,  are  not  yet  answered,  and  farther  investigation  is  required  in 
order  to  fully  establish  the  true  atomic  weight  of  tungsten. 


URANIUM. 

The  earlier  attempts  to  determine  the  atomic  weight  of  uranium  were 
all  vitiated  by  the  erroneous  supposition  that  the  uranous  oxide  was 
really  the  metal.  The  supposition,  of  course,  does  not  affect  the  weigh- 
ings and  analytical  data  which  were  obtained,  although  these,  from  their 
discordance  with  each  other  and  with  later  and  better  results,  have  now 
only  a  historical  value. 

For  present  purposes  the  determinations  made  by  Berzelius,*  by  Arf- 
vedson,f  and  by  Marchand  J  may  be  left  quite  out  of  account.  Berzelius 
employed  various  methods,  while  the  others  relied  upon  estimating  the 
percentage  of  oxygen  lost  upon  the  reduction  of  U3O8  to  U02.  Rammels- 
berg's  §  results  also,  although  very  suggestive,  need  no  full  discussion. 
He  analyzed  the  green  chloride,  UC14;  effected  the  synthesis  of  uranyl 
sulphate  from  uranous  oxide;  determined  the  amount  of  residue  left 
upon  the  ignition  of  the  sodio  and  bario-uranic  acetates;  estimated  the 
quantity  of  magnesium  uranate  formed  from  a  known  weight  of  UO2, 
and  attempted  also  to  fix  the  ratio  between  the  green  and  the  black 
oxides.  His  figures  vary  so  widely  that  they  could  count  for  little  in 
the  establishing  of  any  general  mean ;  and,  moreover,  they  lead  to  esti- 
mates of  the  atomic  weight  which  are  mostly  below  the  true  value.  For 
instance,  twelve  lots  of  USO8  from  several  different  sources  were  reduced 
to  UO2  by  heating  in  hydrogen.  The  percentages  of  loss  varied  from  3.83 
to  4.67,  the  mean  being  4.121.  These  figures  give  values  for  the  atomic 

*Schweigg.  Journ.,  22,  336.     1818.     Poggend.  Annalen,  i,  359.     1825. 
t  Poggend.  Annalen,  i,  245.    Berz.  Jahr.,  3,  120.     1822. 
I  Journ.  fiir  Prakt.  Chem.,  23,  497.     1841. 

g  Poggend.  Annalen,  55,  318,  1842  ;  56,  125,  1842  ;  59,  9,  1843  ;  66,  91,  1845.  Journ.  fiir  Prakt.  Chem., 
29,  324- 


264 


THE    ATOMIC    WEIGHTS. 


weight  of  uranium  ranging  from  184.33  to  234.05,  or,  in  mean,  214.53. 
Such  discordance  is  due  partly  to  impurity  in  some  of  the  material 
studied,  and  illustrates  the  difficulties  inherent  in  the  problem  to  be 
solved.  Some  of  the  uranoso-uranic  oxide  was  prepared  by  calcining  the 
oxalate,  and  retained  an  admixture  of  carbon.  Many  such  points  were 
worked  up  by  Rammelsberg  with  much  care,  so  that  his  papers  should 
be  scrupulously  studied  by  any  chemist  who  contemplates  a  redetermi- 
nation  of  the  atomic  weight  of  uranium. 

In  1841  and  1842  Peligot  published  certain  papers*  showing  that  the 
atomic  weight  of  uranium  must  be  somewhere  near  240.  A  few  years 
qater  the  same  chemist  published  fuller  data  concerning  the  constant  in 
luestion,  but  in  the  time  intervening  between  his  earlier  and  his  final 
researches  other  determinations  were  made  by  Ebelmen  and  by  Wer- 
theim.  These  investigations  we  may  properly  discuss  in  chronological 
order.  For  present  purposes  the  early  work  of  Peligot  may  be  dismissed 
as  only  preliminary  in  character.  It  showed  that  what  had  been  pre- 
viously regarded  as  metallic  uranium  was  in  reality  an  oxide,  but  gave 
figures  for  the  atomic  weight  of  the  metal  which  were  merely  approxi- 
mations. 

Ebelmen 's  f  determinations  of  the  atomic  weight  of  uranium  were 
based  upon  analyses  of  uranic  oxalate.  This  salt  was  dried  at  100°, 
and  then,  in  weighed  amount,  ignited  in  hydrogen.  The  residual  ura- 
nous  oxide  was  weighed,  and  in  some  cases  converted  into  U308  by  heating 
in  oxygen.  The  following  weights  are  reduced  to  a  vacuum  standard  : 

10.1644  grm.  oxalate  gave  7.2939  grm.  UO2. 


12.9985 
11.8007 

9.9923 
11.0887 
10.0830 

6.7940 
16.0594 


9-3312 
8.4690 

7-I73I 
7.9610 

7.2389 
4.8766 
11.5290 


Gain  on  oxidation,  .3685 

.3275 
.2812 
.3105 


•453' 


Reducing  these  figures  to  percentages,  \ve  may  present  the  results  in 
two  columns.     Column  A  gives  the  percentages  of  UO2  in  the  oxalate, 
while  B  represents  the  amount  of  U203  formed  from  100  parts  of  U02 : 
A.      ,  B. 

71-924  

71.787  103.949 

71.767  103.867 

71.621  103.920 

71.794  103.900 

71-793  

71.778 

71.790  103930 


Mean,  71.782,  =b  .019 


Mean,  103.9:3,  =b  .009 


*Compt.  Rend.,  12,  735.     1841.     Ann.  Chim.  Phys.  (3),  55.     1842. 
t  Journ.  fur  Prakt.  Cheni.,  27,  385.     1842. 


URANIUM.  265 

Wertheim's*  experiments  were  even  simpler  in  character  than  those 
of  Ebelmen.  Sodio-uranic  acetate,  carefully  dried  at  200°,  was  ignited, 
leaving  the  following  percentages  of  sodium  uranate  : 

67.51508 
67.54558 
67.50927 

Mean,  67.52331,  ±  .0076 

The  final  results  of  Peligot'sf  investigations  appeared  in  1846.  Both 
the  oxalate  and  the  acetate  of  uranium  were  studied  and  subjected  to 
combustion  analysis.  The  oxalate  was  scrupulously  purified  by  repeated 
crystallizations,  and  thirteen  analyses,  representing  different  fractions, 
were  made.  Seven  of  these  gave  imperfect  results,  due  to  incomplete 
purification  of  the  material;  six  only,  from  the  later  crystallizations, 
need  to  be  considered.  In  these  the  uranium  was  weighed  as  U308,  and 
the  carbon  as  CO2.  From  the  ratio  between  the  C02  and  U308  the  atomic 
weight  of  uranium  may  be  calculated  without  involving  any  error  due 
to  traces  of  moisture  possibly  present  in  the  oxalate.  I  subjoin  Peligot's 
weighings,  and  give,  in  the  third  column,  the  U3O8  proportional  to  100 
parts  of  C02 : 

CO2.  U.A0&.  Ratio. 

.456  grm.  4.649  grm.  319.299 

.369     "  4.412     "  322.279 

2.209     "  7.084     "  320.688 

.019     "  3.279     "  32I-786 

.069     "  3.447     "  322.461 

.052     "  3.389     "  322.148 

Mean,  321.443,  ±  .338 

From  the  acetate,  U02(C2H302)2.2H20,  the  following  percentages  of 
U308  were  obtained : 

5.061  grm.  acetate  gave  3.354  grm.  U3O8.  66.2715  per  cent. 

4.601  "  3-°57  "  66.4421  " 

1.869  "  1.238  "  66.2386  " 

3.817  "  -            2.541  "  66.5706  " 

10.182  "  6.757  "  66.3622  " 

4.393  2.920  "  66.4694  '  " 

2.868  "  1.897  "  66.1437  » 


Mean,  66.3569,  ±  .038 


The  acetate  also  yielded  the  subjoined  percentages  of  carbon  and  of 
water.     Assuming  that  the  figures  for  carbon  were  calculated  from  known 

*  Journ.  fur  Prakt.  Chem.,  29,  209.     1843. 
fCompt.  Rend.,  22,  487.     1846. 


266  THE   ATOMIC    WEIGHTS. 

weights  of  dioxide,  with  C  =  12  and  O  =  16, 1  have  added  a  third  column, 

in  which  the  carbon  percentages  are  converted  into  percentages  of  C02 : 

H.,0.  C.  CO* 

21.60  11.27  4J.323 

21. 16  11.30  41-433 

21.10  11.30  41-433 

2 1. 2O  II.IO  4O.7OO 


Mean,  21.265,  ±  .187       Mean,  11.24  Mean,  41.222,  zh  .092 

From  these  data  we  get  the  following  values  for  the  molecular  weight 
of  uranyl  acetate : 

From  percentage  of  U3O8 423.183,  ±    .4781 

From  percentage  of  CO2 423.842,  =b    .9462 

From  percentage  of  H2O : 420.386,  dr  2.9033 

General  mean • 423.257,  =h    .4222 

In  the  posthumous  paper  of  Zimmermann.  edited  by  Kriiss  and  Alibe- 
goff,*  the  atomic  weight  of  uranium  is  determined  by  two  methods. 
First,  U02,  prepared  by  several  methods,  is  converted  into  U3O8  by  heat- 
ing in  oxygen.  To  begin  with,  U308  was  prepared,  and  reduced  to  U02 
by  ignition  in  hydrogen.  When  the  reduction  takes  place  at  moderate 
temperatures,  the  U02  is  somewhat  pyrophoric,  but  if  the  operation  is 
performed  over  the  blast  lamp  this  difficulty  is  avoided.  After  weighing 
the  UO2,  the  oxidation  is  effected,  and  the  gain  in  weight  observed.  The 
preliminary  U3O8  was  derived  from  the  following  sources :  A,  from  ura- 
nium tetroxide ;  B,  from  the  oxalate ;  C,  from  uranyl  nitrate ;  D,  by 
precipitation  with  mercuric  oxide.  l"he  full  data,  lettered  as  indicated 
above,  are  subjoined : 

UO^,  U-AO%.  Per  cent,  of  Gain. 

8.9363  9.2872  3-927 

7.9659  8.2789  3.929 

12.4385  12.9270  3.927 

f  12.8855  i3-39'3  3.925 

B.  -j    5.7089  5.9331  3.927 

(    9.6270  10.0051  3.928 

13.1855  13-7036  3-929 

9.9973  10.3901  3.929 

15.8996  16.5242  3.928 

7-4326  7.7245  3.927 

Mean,  3.9276,  ±  .0003 
Ebelmen  found,  3.913,    d=  .009 

General  mean,  3.9276,  ±  .0003 

Iii  short,  Ebelmen's  mean  vanishes  when  combined  with    Zimmer 
lann's.  

*  Ann.  d.  Chern.,  232,  299.     1886. 


URANIUM.  267 

Zimmerrnann's  second  method  was  essentially  that  of  Wertheim, 
namely,  the  ignition  of  the  double  acetate  UO2(C2H302)2.NaC2H302,  the 
residue  being  sodium  uranate,  Na2U207. 

Double  Acetate.  Uranate.  Per  cent.  Uranate. 

4.272984  2.886696  67.557 

5.272094  3-560770  67.540 

2.912283  1.967428  67.556 

2.149309  67.555 

Mean,  67.552,  dz  .0027 
Wertheim  found,  67.523,  dz  .0076 


General  mean,  67.549,  dz  .0025 

All  the  data  for  uranium  now  sum  up  thus : 

(i.)  Per  cent.  UO2  from  uranyl  oxalate,  71.782,  dz  .019 

(2.)  6C02  :  U308  :  :  100  :  321.443,  dz  .338 

(3.)  Molecular  weight  of  uranyl  acetate,  423.842,  ±  .4222 

(4.)  3UO2  :  U3O8  :  :  100  :  103.9276,  dz  .0003 

(5.)  Per  cent.  Na2U2O7  from  UO2.Na(C2H3O2)3,  67.549,  dz  .0025 

Computing  with  0  =  15.879,  ±  .0003 ;  C  =  11.920,  ±  .0004,  and  Na  = 
22.881,  ±  .0046,  we  have— 

From  (I) 0  =  235.948,  dz  .1938 

From  (2) ; .  "  =  238.462,  dz  .2953 

From  (3) "  =238.541,  dz-4223 

From  (4) "  =  237.770,  dz  .0055 

From  (5) "  =  237.902,  dz  .0283 


General  mean ...  U  =  237-774,  4=  .0054 

If  0  =  16,  U  =  239.586. 

In  this  case  Zimmermann's  data  control  the  final  result.     All  the  other 
determinations  might  be  rejected  without  appreciable  effect. 


268  THE    ATOMIC    WEIGHTS. 


SELENIUM. 

The  atomic  weight  of  this  element  was  first  determined  by  Berzelius,* 
who,  saturating  100  parts  of  selenium  with  chlorine,  found  that  179  of 
chloride  were  produced.  Further  on  these  figures  will  be  combined  with 
similar  results  by  Dumas. 

We  may  omit,  as  unimportant  for  present  purposes,  the  analyses  of 
alkaline  selenates  made  by  Mitscherlich  and  Nitzsch.  f  and  pass  on  to 
the  experiments  published  by  Sacc  J  in  1847.  This  chemist  resorted  to 
a  variety  of  methods,  some  of  which  gave  good  results,  while  others  were 
unsatisfactory.  First,  he  sought  to  establish  the  exact  composition  of 
Se02,  both  by  synthesis  and  by  analysis.  The  former  plan,  according  to 
which  he  oxidized  pure  selenium  by  nitric  acid,  gave  poor  results ;  better 
figures  were  obtained  upon  reducing  Se02  with  ammonium  bisulphite 
and  hydrochloric  acid,  and  determining  the  percentage  of  selenium  set 
free : 

.6800  grm.  SeO2  gave    .4828  grm.  Se.  71.000  per  cent. 

3.5227  "  2.5047        "  71.102        " 

4.4870  3-193°       "  71.161        " 

Mean,  71.088,  ±  .032 

In  a  similar  manner  Sacc  also  reduced  barium  selenite,  and  weighed 
the  resulting  mixture  of  barium  sulphate  and  free  selenium.  This  pro- 
cess gave  discordant  results,  and  a  better  method  was  found  in  calcining 
BaSe03  with  sulphuric  acid,  and  estimating  the  resulting  quantity  of 
BaSO4.  In  the  third  column  I  give  the  amounts  of  BaS04  equivalent  to 
100  of  BaSe03 : 

•5573  grm-  BaSeO3  gave  .4929  grm.  BaSO4.  88.444 

.9942                  »                .8797           "  88.383 

.2351                  "                .2080           "  88.473 

.9747                  "                .8621            "  88.448 


Mean,  88.437,  ±  .013 

Still  other  experiments  were  made  with  the  selenites  of  silver  and  lead  ; 
but  the  figures  were  subject  to  such  errors  that  they  need  no  further  dis- 
cussion here. 

A  few  years  after  Sacc's  work  was  published,  Erdmann  and  Marchand 
made  with  their  usual  care  a  series  of  experiments  upon  tHe  atomic 
weight  under  consideration.  §  They  analyzed  pure  mercuric  selenide, 
which  had  been  repeatedly  sublimed  and  was  well  crystallized.  Their 

*  Poggend.  Annalen,  8,  i.     1826. 

t  Poggend.  Annaleu,  9,  623.     1827.  t 

}  Ann.  d.  Chim.  et  d.  Phys.  (3),  21,  119. 

I  Jour,  fiir  Prakt.  Chem.,  55,  202.     1852. 


SELENIUM.  269 

method  of  manipulation  has  already  been  described  in  the  chapter  upon 
mercury.     These  percentages  of  Hg  in  HgSe  were  found  : 

71.726 

7r-73i 

71.741 


Mean,  71.7327,  ±.003 

The  next  determinations  were  made  by  Dumas,*  who  returned  to  the 
original  method  of  Berzelius.  Pure  selenium  was  converted  by  dry 
chlorine  into  SeCl4,  and  from  the  gain  in  weight  the  ratio  between  Se 
and  Cl  was  easily  deducible.  I  include  Berzelius'  single  experiment, 
which  I  have  already  cited,  and  give  in  a  third  column  the  quantity  of 
chlorine  absorbed  by  100  parts  of  selenium  : 

.709  grm.  Se  absorb  3.049  grm.  Cl.  178.409 

.810  "  3.219       "  177.845 

.679  "  3.003        "  178.856 

.498  "  2.688       "  179-439 

•  944  "  3.468       "  178.395 

.887  "  3.382       "  179.226 

•935  "  3.452       "  178.398 

1 79.000 — Berzelius. 

Mean,  178.696,  ±  .125 

The  question  may  here  be  properly  asked,  whether  it  would  be  possi- 
ble thus  to  form  SeCl4,  and  be  certain  of  its  absolute  purity  ?  A  trace  of 
oxychloride,  if  simultaneously  formed,  would  increase  the  apparent 
atomic  weight  of  selenium.  In  point  of  fact,  this  method  gives  a  higher 
value  for  Se  than  any  of  the  other  processes  which  have  been  adopted, 
and  that  value  has  the  largest  probable  error  of  any  one  in  the  entire 
series.  A  glance  at  the  table  which  summarizes  the  discussion  at  the 
end  of  this  chapter  will  render  this  point  sufficiently  clear. 

Still  later.  Ekman  and  Pettersson  f  investigated  several  methods  for 
the  determination  of  this  atomic  weight,  and  finally  decided  upon  the 
two  following  : 

First,  pure  silver  selenite,  Ag.2Se03  was  ignited,  leaving  behind  metallic 
silver,  which,  however,  sometimes  retained  minute  traces  of  selenium. 
The  data  obtained  were  as  follows  : 

Ag^SeO^.  Ag.  Per  cent.  Ag. 

5.2102  3-2787  62-93 

5.9721  3-7597  62.95 

7.2741  4-5803  62.97 

7.5390  4.7450  62.94 

6.9250  4.3612  62.98 

7.3455  4.6260  62.98 

6.9878  4.3992  62.95 

Mean,  62.957,  d=  .005 

*Ann.  Chetn.  Pharm.,  113,  32.     1860. 

-f  Ber.  d.  Deutsch.  Chem.  Gesell.,  9,  1210.     1876.     Published  in  detail  by  the  society  at  Upsala. 


270  THE    ATOMIC    WEIGHTS. 

Secondly,  a  warm  aqueous  solution  of  selemous  acid  was  mixed  with 
HC1,  and  reduced  by  a  current  of  S02.  The  reduced  Se  was  collected 
upon  a  glass  filter,  dried,  and  weighed. 

SeO.2,  Se.  Per  cent.  Se. 

11.1760  7-9573  7i.i99 

11.2453  8.0053  7I-J85 

24.4729  17-4232  7i.i93 

208444  i  4-  8383  71.187 

31.6913  22.5600  7i-I9I 

Mean,  71.191,     ±  .0016 
Sacc  found,  71.088,    db  .0320 


General  mean,  71.1907,  rb  .0016 

There  are  now  five  series  of  figures  from  which  to  deduce  the  atomic 
weight  of  selenium  : 

(I.)  Per  cent,  of  Se  in  SeO2,  71.1907,  ±  *ooi6 

(2.)  BaSeO3  :  BaSO4  :  :  100  :  88.437,  ±  .013 

(3.)  Per  cent,  of  Hg  in  HgSe,  71.7327,  d=  .003 

(4.)  Se  :  C14  :  :  100  :  178.696,  ±  .125 

(5.)  Per  cent,  of  Ag  in  Ag2SeO3,  62.957,  ±  .005 

From  these,  computing  with — 

O   =   15.879,  dz  .0003  s    =  31.828,  ±  .0015 

Ag  =  107.108,  ±  .0031  Ba   =  136.392,  ±  .0086 

Cl   =    35.179,  rb  .0048  Hg  3=  198.491,  dz  .0083, 

five  values  for  Se  are  calculable,  as  follows : 

From  (i) Se  =  78.477,  dc  .0049 

From  (2) , "  i=  78.006,  ±  .0410 

From  (3) "  =  78.217,  ±  .0095 

From  (4) "  =  78.740,  ±  .0561 

From  (5) "  =  78.405,  ±  .0201 


General  mean Se  =  78.419,  ±  .0042 

If  0  =  16,  this  becomes  Se  =  79.016. 


TELLURIUM.  271 


TELLURIUM. 

Particular  interest  attaches  to  the  atomic  weight  of  tellurium  on  ac- 
count of  its  relations  to  the  periodic  law.  According  to  that  law,  tellurium 
should  lie  between  antimony  and  iodine,  having  an  atomic  weight  greater 
than  120  and  less  than  126.  Theoretically,  Mendelejeff  assigns  it  a  value 
of  Te  =  125.  but  all  of  the  best  determinations  lead  to  a  mean  number 
higher  than  is  admissible  under  the  currently  accepted  hypotheses. 
Whether  theory  or  experiment  is  at  fault  remains  to  be  discovered. 

The  first,  and  for  many  years  the  only,  determinations  of  the  constant 
in  question  were  made  by  Berzelius.*  By  means  of  nitric  acid  he  oxi- 
dized tellurium  to  the  dioxide,  and  from  the  increase  in  weight  deduced 
a  value  for  the  metal.  He  published  only  his  final  results,  from  which, 
if  O  =  100,  Te  =  802.121.  The  three  separate  experiments  give  Te  = 
801.74,  801.786,  and  802.838,  whence  we  can  calculate  the  following  per- 
centages of  metal  in  the  dioxide  : 

80.057 

80.036 

80.034 

Mean,  80.042,  ±  .005 

The  next  determinations  were  made  by  von  Hauer,f  who  resorted  to 
the  analysis  of  the  well  crystallized  double  salt  TeBr4.2KBr.  In  this 
compound  the  bromine  was  estimated  as  silver  bromide,  the  values 
assumed  for  Ag  and  Br  being  respectively  108.1  and  80.  Recalculating, 
with  our  newer  atomic  weights  for  the  above-named  elements,  we  get 
from  von  Hauer's  analyses,  for  100  parts  of  the  salt,  the  quantities  of  AgBr 
which  are  put  in  the  third  column  : 

2.000  grm.  K2TeBr6  gave  69.946  per  cent.  Br.  164.460 

6.668  "  69.8443         "  164.221 

2.934  69.9113         "  164.379 

3.697  "  70.0163         "  164.626 

i.  ooo  "  69.901          "  164.355 

Mean,  164.408,  =b  .045 

From  Berzelius'  series  we  may  calculate  Te  =  127.366,  and  from  von 
Hauer's  Te  =  126.454.  Dumas,  J  by  a  method  for  which  he  gives  abso- 
lutely no  particulars,  found  Te  =  129. 

In  1879,  with  direct  reference  to  Mendelejeff 's  theory,  the  subject  of 
the  atomic  weight  of  tellurium  was  taken  up  by  Wills.  §  The  methods 

*Poggend.  Annalen,  28,  395.     1833. 
t  Sitzungsb.  Wien  Akad.,  25,  142. 
j  Ann.  Chim.  Phys.  (3),  55,  129.     1859. 
I  Journ.  Chem.  Soc.,  Oct.,  1879,  p.  704. 


272  THE    ATOMIC    WEIGHTS. 

of  Berzelius  and  von  Hauer  were  employed,  with  various  rigid  precau- 
tions in  the  way  of  testing  balance  and  weights,  and  to  ensure  purity  of 
material.  In  the  first  series  of  experiments  tellurium  was  oxidized  by 
nitric  acid  to  form  Te02.  The  results  gave  figures  ranging  from  Te  = 
125.64  to  128.66 : 

2.21613  grm.  Te  gave  2.77612  grm.  TeO2.  79.828  per  cent.  Te. 

1.45313  1.81542         "  80.044  " 

2.67093  "  3-33838         "  80.007 

477828  "  5.95748         "  80.207  " 

2.65029  "  3-3I331          "  79-989 


Mean,  80.015,  ±  .041 

In  the  second  series  tellurium  was  oxidized  by  aqua  regia  to  Te02,  with 
results  varying  from  Te  ==  127.10  to  127.32  : 

2.85011  grm.  Te  gave  3.56158  grm.  TeO2.  80.024  per  cent.  Te. 

3.09673  3-86897          "  80.040  " 

5-°9365  "  6.36612         "  80.012  " 

3.26604  4.08064         "  80.037  " 

Mean,  80.028,  ±  .004 

By  von  Hauer's  process,  the  analysis  of  TeBr4.2KBr,  Will's  figures  give 
results  ranging  from  Te  =  125.40  to  126.94.  Reduced  to  a  common 
standard,  100  parts  of  the  salt  yield  the  quantities  of  AgBr  given  in  the 
third  column  : 

1.70673  grm.  K2TeBr6  gave  2.80499  grm.  AgBr.  164.349 

1.75225                  "                  2.88072         "  .164.398 

2.06938                 "                  3-40739         "  164.657 

3.29794                                     5-43228         "  164.717 

2.46545                  "                  405742         "  164.571 


Mean,  164.538,  ±  .048 

Combined  with  von  Hauer's  mean,  164.408,  ±  .045,  this  gives  a  general 
mean  of  164.468,  ±  .033.  Hence  Te  =  126.502. 

The  next  determinations  in  order  of  time  were  those  of  Brauner.* 
This  chemist  tried  various  unsuccessful  methods  for  determining  the 
atomic  weight  of  tellurium,  among  them  being  the  synthetic  preparation 
of -silver,  copper,  and  gold  tellurides,  and  the  basic  sulphate,  Te2S07. 
None  of  these  methods  gave  sufficiently  concordant  results,  and  they 
were  therefore  abandoned.  The  oxidation  of  tellurium  to  dioxide  by 
means  of  nitric  acid  was  also  unsatisfactory,  but  a  series  of  oxidations 
with  .aqua  regia  gave  data  as  follows.  The  third  column  contains  the 
percentage  of  tellurium  in  the  dioxide : 

*  Journ.  Chem.  Soc.,  55,  382.     1889. 


TELLURIUM.  273 

Te.  TeO.2.  Percent.  Te. 

2.3092  2.9001  79.625' 

2-8153  3-5332  79-68i 

4.0176  5-°347  79-798 

3.1613  3-9685  79.660 

.8399  1.0526  79-793 

Mean,  79.711,  ±  .0239 

Hence  Te  =  124.709. 

In  a  single  analysis  of  the  dioxide,  by  reduction  with  S02,  2.5489 
grammes  Te02  gave  2.0374  of  metal.  If  we  give  this  experiment  the 
weight  of  one  observation  in  the  synthetic  series,  the  percentage  of  tel- 
lurium found  by  it  becomes — 

79.932,  ±  -0534. 
Hence  Te  =  126.494. 

Brauner's  best  results  were  obtained  from  analyses  of  tellurium  tetra- 
bromide,  prepared  from  pure  tellurium  and  pure  bromine,  and  after- 
wards sublimed  in  a  vacuum.  This  compound  was  titrated  with  standard 
solutions  of  silver,  and  three  series  of  experiments,  made  with  samples 
of  bromide  of  different  origin,  gave  results  as  follows.  The  TeBr4  equiva- 
lent to  100  parts  of  silver  appears  in  the  third  column  : 

First  Series. 

TeBr^.  Ag±.  Ratio. 

2.14365  2.06844  103.636 

1.76744  1.70531  103.643 

1.47655  1.42477  103.634 

1.23354  1.19019  103.642 

Second  Series. 

TeBr±.  Ag±.  Ratio. 

3.07912  2.97064  103.651 

5.47446  5-28i57  103.652 

3-30927  3.I93I3  103.637 

7.26981  7.01414  103.645 

3.52077  3-39667  103.654 

Third  Series. 
TeBr±.  Ag±.  Ratio. 

2.35650  2.27363  103.645 

1.51931  1.46564  103.662 

1.43985  1.38942  103.630 


Mean  of  all  as  one  series,  103.644,  ±  .0018 
18 


274  THE    ATOMIC   WEIGHTS. 

Hence  Te  =  126.668,  ±  .0290.  A  reduction  of  the  weighings  to  a 
vacuum  raises  this  by  0.07  to  126.738. 

Still  another  series  of  analyses,  made  with  fractionated  material,  gave 
values  for  tellurium  running  up  to  as  high  as  137.  These  experiments 
led  Brauner  to  believe  that  he  had  found  in  tellurium  a  higher  homo- 
logue  of  that  element,  a  view  which  he  has  since  abandoned.*  Brauner 
also  made  a  series  of  analyses  of  tellurium  dibromide,  but  the  results 
were  unsatisfactory. 

In  the  series  of  determinations  by  Gooch  and  Rowland  f  an  alkaline 
solution  of  tellurium  dioxide  was  oxidized  by  means  of  standard  solu- 
tions of  potassium  permanganate.  This  was  added  in  excess,  the  excess 
being  measured,  after  acidification  with  sulphuric  acid,  by  back  titration 
with  oxalic  acid  and  permanganate.  Two  series  are  given,  varying  in 
detail,  but  for  present  purposes  they  may  be  treated  as  one.  The  ratio 
Te02 :  0  :  :  100  :  x  is  given  in  the  third  column. 

TeO-i  Taken.  O  Required.  Ratio. 

.1200  .01202  10.017 

.0783  .00785  10.026 

.0931  .00940  10.097 

'  .1100  .01119  10.149 

.0904  .00909  10.055 

.1065  .01078  10.122 

.0910  -00915  10055 

.0910  .00910  lo.ooo 

.0911  .00924  10.143 

.0913  .00915  IO.O22 

.09I2  -00915  10.033 

.0914  .00923  10.098 

Mean,  10.068,  ±  .0100 

Hence  Te  =  125.96. 

In  Staudenmaier's  \  determinations  of  the  atomic  weight  of  tellurium, 
crystallized  telluric  acid,  H6Te06  was  the  starting  point.  By  careful 
heating  in  a  glass  bulb  this  compound  can  be  reduced  to  Te02,  and  by 
heating  in  hydrogen,  to  metal.  In  the  latter  case  finely  divided  silver  was 
added  to  prevent  volatilization  of  tellurium.  The  telluric  acid  was  frac- 
tionally crystallized,  but  the  different  fractions  gave  fairly  constant  results. 
I  therefore  group  Staudenmaier's  data  so  as  to  bring  them  into  series 
more  suitable  for  the  present  discussion. 

*  Journ.  Chem.  Soc.,  67,  549.     1895. 

f  Atfler.  Journ.  Sci.,  58,  375.  1894.  Some  misprints  in  the  original  publication  have  been  kindly 
corrected  by  Professor  Gooch  ;  hence  the  differences  between  these  data  and  the  figures  formerly 
given. 

JZeitseh.  Anorg.  Chem.,  10,  189.     1895. 


TELLURIUM.  275 

First.  H6Te06  to  Te0.2. 

Loss  in  Weight.  Per  cent.  TeO.2. 

1.7218  .5260  69.451 

2.8402  .8676  69.453 

4.0998  1.2528  69.442 

3.0916  .9450  69.433 

1.1138  .3405  69.429 

4.9843  1.5236  69.432 

4.6716  1.4278  69.437 


Mean,  69.440,  ±  .0024 

Hence  Te  =  126.209. 

Second.  H6Te06  to  Te. 

//67><96.                     Loss  hi  Weight.  Percent.  Te. 

1.2299                                 .5471  55.517 

1.0175                                  -4526  55-5'S 

2.5946                                I.I549  55-488 


Mean,  55.508,  ±  .0068 

Hence  Te  =  126.303. 

Staudenmaier  also  gives  four  reductions  of  Te02  to  Te,  in  presence  of 
finely  divided  silver.  The  data  are  as  follows  : 

.  7><9.2.  Loss  in  Weight.  Per  cent.  Te. 

.9171  .1839  79.948 

i  9721  .3951  79.966 

2-4115  -4835  7995° 

1.0172  .2041  79-935 

Mean,  79.950,  ±  .0043 

Hence  Te  =  126.636. 

The  last  series,  giving  the  percentage  of  tellurium  in  the  dioxide,  com- 
bines with  previous  series  thus  : 

Berzelius 80.042,  ±  .0050 

Wills,  first  series 80.015,  d=  .0410 

Wills,  second  series 80.028,  ±  .0040 

Brauner,  synthesis 79. 7  r  I ,  ±  .0239 

Brauner,  analysis 79-932,  ±  .°534 

Staudenmaier 79-95°i  ±  .004  3 

General  mean 80.001,  =t  .0025 

The  very  recent  determinations  byChikashige*  were  made  by  Brauner's 
method,  giving  the  ratio  between  silver  and  TeBr4.  In  all  essential  par- 
ticulars the  work  resembles  that  of  Brauner.  except  that  the  tellurium, 

*  Journ.  Chetn.  Soc.,  69,  8Si.     1896. 


276  THE    ATOMIC    WEIGHTS. 

instead  of  being  extracted  from  metallic  tellurides,  was  derived  from 
Japanese  native  sulphur,  in  which  it  exists  as  an  impurity.  This  differ- 
ence of  origin  in  the  material  studied  gives  the  chief  interest  to  the 
investigation.  The  data  are  as  follows  : 


Ag.  Ratio. 

4.1812                              4.0348  103.628 

4.3059                              4-1547  103.639 

4.5929                                4.43!9  103.633 


Mean,  103.633,  ±.0023 
Brauner  found,  103.644,  ±  .0018 


General  mean,  103.640,  it  .0014 

Now,  to  sum  up,  the  subjoined  ratios  are  available  for  computing  the 
atomic  weight  of  tellurium  : 

(I.)  Percentage  Te  in  TeO2,  80.001,  =b  .0025 
(2.)   Percentage  Te  in  H6TeO6,  55.508,  ±  .0068 
(3.)   Percentage  TcO2  in  H6TeO6,  64.440,  ±  .0024 
(4.)   Ag4  :  TeBr4  :  :  100  :  103.640,  ±  .0014 
(5.)   K2TeBrg  :  6AgBr  :  :  100  :  164.468,  =b  .0330 
(6.)  TeO2  :  O  :  :  100  :  10.068,  =b  .0100 

To  reduce  these  ratios  we  have — 

O  =  15.879,^.0003  K    =  38.817,  ±  .0051 

Ag  =»  107.108,  ±  .0031  AgBr  =  186.452,  rb  .0054 

Br  =  ::  79-344,  ±.  -0062 

For  the  atomic  weight  of  tellurium  six  values  appear,  as  follows : 

From  (i) Te  =  127.040,  ±  .0165 

From  (4) "    =  126.650,  rb  .0302 

From  (5) "    =  126.502,1^.1430 

From  (2) "    =126.303,^.0246 

From  (3) "    =  126.209,  zb  .0138 

From  (6) "    =  125.960,^.1574 


General  mean Te  =  126.523,  rb  .0092 

If  0  =  16,  Te  =  127.487. 

A  careful  consideration  of  the  foregoing  figures,  and  of  the  experi- 
mental methods  by  which  they  were  obtained,  will  show  that  they  are 
not  absolutely  conclusive  with  regard  to  the  place  of  tellurium  under 
the  periodic  law.  The  atomic  weight  of  iodine,  calculated  in  a  previous 
chapter,  is  125.888.  Wills1  values  for  Te,  rejecting  his  first  series  as  rela- 
tively unimportant,  range  from  125.40  to  127.32  ;  that  is,  some  of  them 
fall  below  the  atomic  weight  of  iodine,  although  none  descend  quite  to 
the  125  assumed  by  Mendelejeff. 

Some  of  Brauner's  data  fall  even  lower;  and  the  same  thing  is  true  in 


FLUORINE.  277 

Gooch  and  Rowland's  series,  of  which  the  mean  gives  Te  =  125.96,  a 
value  very  little  above  that  of  iodine. 

In  considering  the  experimental  methods,  reference  may  properly  be 
made  to  the  controversy  regarding  the  atomic  weight  of  antimony.  It 
will  be  seen  that  Dexter,  estimating  the  latter  constant  by  the  conver- 
sion of  the  metal  into  Sb204,  obtained  a  value  approximately  of  Sb  =  122. 
Dumas,  working  with  SbCl3,  obtained  nearly  the  same  value.  Schneider 
and  Cooke,  on  the  other  hand,  have  established  an  atomic  weight  for 
antimony  near  120,  and  Cooke  in  particular  has  traced  out  the  constant 
errors  which  lurked  unsuspected  in  the  work  of  Dumas.  Now  in  their 
physical  aspects  tellurium  and  antimony  are  quite  similar.  The  oxida- 
tion of  tellurium  to  dioxide  resembles  in  many  particulars  that  of  anti- 
mony, and  may  lead  to  error  in  the  same  way.  In  each  of  the  six  tel- 
lurium ratios  there  is  still  uncertainty,  and  a  positive  measurement,  free 
from  objections,  of  the  constant  in  question  is  yet  to  be  made. 


FLUORINE. 

The  atomic  weight  of  fluorine  has  been  chiefly  determined  by  one 
general  method,  namely,  by  the  conversion  of  fluorides  into  sulphates. 
The  work  of  Christensen,  however,  is  on  different  lines.  Excluding  the 
early  results  of  Davy,*  we  have  to  consider  first  the  experiments  of 
Berzelius,  Louyet,  Dumas,  De  Luca,  and  Moissan  with  reference  to  the 
fluorides  of  calcium,  sodium,  potassium,  barium,  and  lead. 

The  ratio  between  calcium  fluoride  and  sulphate  has  been  determined 
by  the  five  investigators  above  named,  and  by  one  general  process.  The 
fluoride  is  treated  with  strong  sulphuric  acid,  the  resulting  sulphate  is 
ignited,  and  the  product  weighed.  In  order  to  insure  complete  trans- 
formation special  precautions  are  necessary,  such,  for  instance,  as  re- 
peated treatment  with  sulphuric  acid,  and  so  on.  For  details  like  these 
the  original  papers  must  be  consulted. 

The  first  experiments  in  chronological  order  are  those  of  Berzelius,f 
who  operated  upon  an  artificial  calcium  fluoride.  He  found,  in  three 
experiments,  for  one  part  of  fluoride  the  following  of  sulphate  : 

1-749 
1.750 
I-75I 

Mean,  1.750,  ±  .0004 

Louyet's  researches  J  were  much  more  elaborate  than  the  foregoing. 
He  began  with  a  remarkably  concordant  series  of  results  upon  fluor  spar, 

*  Phil.  Trans.,  1814,  64. 

f  Poggend.  Annalen,  8,  i.     1826. 

I  Ann.  Chim.  Phys.  (3),  25,  300.     1849. 


278  THE   ATOMIC   WEIGHTS. 

•in  which  one  gramme  of  the  fluoride  yielded  from  1.734  to  1.737  of  sul- 
phate. At  first  he  regarded  these  as  accurate,  but  he  soon  found  that 
particles  of  spar  had  been  coated  with  sulphate,  and  had  therefore 
escaped  action.  In  the  following  series  this  source  of  error  was  guarded 
against. 

Starting  with  fluor  spar,  Louyet  found  of  sulphate  as  follows: 

.742 

•  744 

•  745 

•  744 

•  7435 
•7435 


Mean,  1.7437,  ±  .0003 


A  second  series,  upon  artificial  fluoride,  gave  : 

i.743 
1.741 


Mean,  1.7417,  ±  .0004 

Dumas  *  published  but  one  result  for  calcium  fluoride.  .495  grm.  gave 
.864  grm.  sulphate,  the  ratio  being  1  : 1.7455. 

De  Lucaf  worked  with  a  very  pure  fluor  spar,  and  published  the  fol- 
lowing results.  The  ratio  between  CaS04  and  one  gramme  of  CaF2  is 
given  in  the  third  column  : 


.9305  grm.  CaF2  gave  1.630  grm.  CaSO4. 

.836       "       1.459     "  1.7452 

.502       "       .8755    "  1.7440 

.3985      "       .6945    "  1.7428 

If  we  include  Dumas'  single  result  with  these,  we  get  a  mean  of 
1.7459,  ±  .0011. 

MoissanJ  unfortunately  gives  no  details  nor  weighings,  but  merely 
states  that  four  experiments  with  calcium  fluoride  gave  values  for  F  rang- 
ing from  19.02  to  19.08.  To  S  he  assigned  the  value  32.074,  and  probably 
Ca  was  taken  as  —  40.  With  these  data  his  extreme  values  as  given 
may  be  calculated  back  into  uniformity  with  the  ratio  as  stated  above, 
becoming — 

1-7444 
1.7410 


Mean,  1.7427 


*Ann.  Chem.  Pharm.,  113,  28. 
t  Compt.  Rend.,  51,  299.  1860. 
I  Compt.  Rend  ,  in,  570.  1890. 


FLUORINE.  279 

If  we  assign  this  equal  weight  with  Berzelius'  series,  the  data  for  this 
ratio  combine  thus  : 

Berzelius 1.7500,  ±  .0004 

Louyet,  first  series 1.7437,  ±  .0003 

Louyet,  second  series 1.7417,  ±  .0004 

De  Luca  with  Dumas 1.7459,  ±  .0011 

Moissan 1.7427,  ±  .0004 


General  mean 1.7444,  ±  .00018 

For  the  ratio  between  the  two  sodium  salts  we  have  experiments  by 
Dumas,  Louyet,  and  Moissan.  According  to  Louyet,  one  gramme  of 
NaF  gives  of  Na2S04— 

1.686 

1.683 

1.685 


Mean,  1.6847,  ±  .0006 

The  weighings  published  by  Dumas  are  as  follows  : 

.777  grm.  NaF  give  1.312  grm.  Na2SO4.  Ratio,  1.689 

1.737  "  2.930  "  "        1.687 

Mean,  1.688,  ±  .0007 

Moissan  says  only  that  five  experiments  with  sodium  fluoride  gave 
.   F  =  19.04  to  19.08.    This  was  calculated  with  Na  =  23.05  and  S'=  32.074. 
Hence,  reckoning  backward,  the  two  values  give  for  the  standard  ratio — 


1.6873 

Mean,  1.6881 

Giving  this  equal  weight  with  Dumas'  mean,  we  have — 

Louyet 1 .6847,  =fc  .0006 

Dumas 1.688,    ±  .0007 

Moissan 1.6881,  ±  .0007 


General  mean 1 .6867,  ±  .00038 

Dumas  also  gives  experiments  upon  potassium  fluoride.  The  quantity 
of  sulphate  formed  from  one  gramme  of  fluoride  is  given  in  the  last 
column : 

1.483  grm.  KF  give  2.225  grm-  K2SO4.  1.5002 

1.309  "  1.961  "  1.4981 

•    Mean,  1.499^  ±  .0007 

The  ratio  between  barium  fluoride  and  barium  sulphate  was  measured 


280  THE   ATOMIC    WEIGHTS. 

by  Louyet  and  Moissan.     According  to  Louyet,  one  gramme  of  BaF., 
gives  of  BaS(\ — 

L332 

1.331 

1.330 

Mean,  1.331,  =b  .0004 

Moissan,  in  five  experiments,  found  F  —  19.05  to  19.09.  Assuming 
that  he  put  Ba  =  137,  and  S— 32.074  as  before,  these  two  extremes 
become — 


1-3305 
Mean,  1.3308 

Giving  this  equal  weight  with  Louyet's  mean,  we  get  the  subjoined 
combination : 

Louyet I-33I,    ±.0004 

Moissan 1 .3308,  db  .0004 


General  mean i-33°9>  ±  .00028 

The  experiments  with  lead  fluoride  are  due  to  Louyet,  and  a  new 
method  of  treatment  was  adopted.  The  salt  was  fused,  powdered,  dis- 
solved in  nitric  acid,  and  precipitated  by  dilute  sulphuric  acid.  The 
evaporation  of  the  fluid  and  the  ignition  of  the  sulphate  was  then  effected 
without  transfer.  Five  grammes  of  fluoride  were  taken  in  each  opera- 
tion, yielding  of  sulphate : 

6.179 

6.178 

6.178 

Mean,  6.1783,  d=  .0002 

In  Christensen's  determinations*  we  find  a  method  adopted  which  is 
radically  unlike  anything  in  the  work  of  his  predecessors.  He  started 
out  with  the  salt  (NH4)2MnF5.  When  this  is  added  to  a  mixture,  in 
solution,  of  potassium  iodide  and  hydrochloric  acid,  iodine  is  set  free, 
and  may  be  titrated  with  sodium  thiosulphate.  One  molecule  of  the 
salt  (as  written  above),  liberates  one  atom  of  iodine.  In  four  experi- 
ments Christensen  obtained  the  following  data : 

3.1199  grm.  Am.2MnF5  gave  2.12748  I.  68.191  per  cent. 

3.9190  "                    2.67020  "  68.135        " 

3.5005  "                    2.38429  "  68.113        " 

1.2727  "                      .86779  "  68.185        " 

Mean,  68.156,  ±  .0128 

*  Journ.  fiir  Prakt.  Chem.  (2),  35,  541.     Christensen  assigns  to  the  salt  double  the  formula  here 
given. 


FLUORINE.  2j31 

The  ratios  from  which  to  compute  the  atomic  weight  of  fluorine  are 
now — 

(I.)   CaF2  :  CaSO4  :  :  i.o  :  1.7444,  ±  .00018 
(2.)   2NaF  :  Na2SO4  :  :  i.o  :  1.6867,  ±  .00038 
(3.)   2KF  :  K2SO4  :  :  i.o  :  1.4991,  ±  .0007 
(4.)   BaF2  :  BaSO4  :  :  i.o  :  1.3309,  ±  .00028 
(5.)   PbF2  :  PbSO4  :  :  5.0  :  6.1783,  ±  .0002 
(6.)  Am2MnF5  :  I  :  :  100  :  68.156,  ±  .0128 

To  reduce  them  we  have — 

0  —    l5-&79,  db  .0003  K   —   38.817,  dr  .0051 

S  =  31.828,  ±  .0015  Ca  =  39.764,  =h  .0045 

N  =  13.935,  =t  .0021  Ba  =  136.392,  zfc  .0086 

1  —  125.888,  ±  .0069  Pb  =  205.358,  ±  .0040 
Na  —  22.881,  rh  .0046  Mn=  54-571,  i:  .0013 

And  the  values  derived  for  fluorine  are  as  follows: 

From  (i) F=  18.844,  d- .0048 

From  (2) "  =  18.948,  dr  .0108 

From  (31 "  =  18.877,  ±  .0276 

From  (4) "  =  18.869,  ±  .0192 

From  (5) "  =  18.997,  dr  .0047 

From  (6) "  =  18.853,  ±  .0073 


General  mean F  =  18.912,  ±  .0029 

If  O  =  16,  F  =  19.056. 

In  all  probability  these  values  for  fluorine  average  a  trifle  too  high. 
It  is  difficult  to  be  certain  that  a  fluoride  has  been  completely  converted 
into  sulphate,  and  an  incomplete  conversion  tends  to  raise  the  apparent 
atomic  weight  of  fluorine.  This  possible  source  of  error  exists  in  all  of 
the  ratios  except  the  last  one,  but  the  fair  concordance  of  the  results 
obtained  seems  to  indicate  that  the  uncertainty  cannot  be  very  large. 


282  THE   ATOMIC   WEIGHTS. 


MANGANESE. 

The  earliest  experiments  of  Berzelius*  and  of  Arfvedsonf  gave  values 
for  Mn  ranging  between  56  and  57,  and  therefore  need  no  farther  con- 
sideration here.  The  first  determinations  to  be  noticed  are  those  of 
Turner  J  and  a  later  measurement  by  Berzelius.§  who  both  determined 
gravimetrically  the  ratio  between  the  chlorides  of  manganese  and  silver. 
The  manganese  chloride  was  fused  in  a  current  of  dry  hydrochloric  acid, 
and  afterwards  precipitated  with  a  silver  solution.  I  give  the  MnCl2 
equivalent  to  100  parts  of  AgCl  in  the  third  column : 

4.20775  grm.  MnG2==    9.575    grm.  AgCl.  43-945  \ 

,  _        _  > 

3.063  =  6.96912  43-95°-' 

12.47       grains  MnQ2  =    28.42  grains  AgCl.  43.878 — Turner. 

Mean,  43.924,  ±  .015 

Many  years  later  Dumas  ||  also  made  the  chloride  of  manganese  the 
starting  point  of  some  atomic  weight  determinations.  The  salt  was  fused 
in  a  current  of  hydrochloric  acid,  and  afterwards  titrated  with  a  standard 
solution  of  silver  in  the  usual  way.  One  hundred  parts  of  Ag  are  equiva- 
lent to  the  quantities  of  MnCl2  given  in  the  third  column : 

3.3672  grm.  MnCl2  =  5.774  grm.  Ag.  58-3i7 

3.0872  "  5.293         "  58.326 

2.9671  "  5-0875       "  58.321 

1.1244  1.928         "  58.320 

1.3134  "  2.251          "  58.321 

Mean,  58.321,  =h  .001 

An  entirely  different  method  of  investigation  was  followed  by  von 
Hauer,^]"  who,  as  in  the  case  of  cadmium,  ignited  the  sulphate  in  a  stream 
of  sulphuretted  hydrogen,  and  determined  the  quantity  of  sulphide  thus 
formed.  I  subjoin  his  weighings,  and  also  the  percentage  of  MnS  in 
MnS04  as  calculated  from  them  : 

4.0626  grm.  Mn?O4  gave  2.3425  grm.  MnS.  57-66o  per  cent. 

4.9367  "  2.8442  "  57.613       " 

5.2372  "  3-OI92  "  57.649       c< 

7.0047  "  4.0347  "  57.600       " 

4.9175  "  2.8297  "  57-543 

4-8546  "•  2.7955  »  57.585       " 

4.9978  2.8799  "  57.625 

4  6737  "  2.6934  "  57.629 

4.7240  2.7197  "  57.572 

Mean,  57.608,  =fc  .008 


*  Poggend.  Anualen,  8,  185.     1826. 

t  Berz.  Jahresbericht,  9,  136.     1829. 

| Trans.  Roy.  Soc.  Ediub.,  ir,  143.     1831. 

I  Lehrbuch,  5  Aufl.,  3.  1224. 

||  Ann.  Chem.  Pharm.,  113,  25.     1860. 

If  Journ.  fur  Prakt.  Chem.,  72,  360.     1857. 


MANGANESE.  283 

This  method  of  von  Hauer,  which  seemed  to  give  good  results  with 
cadmium,  is,  according  to  Schneider,*  inapplicable  to  manganese,  for  the 
reason  that  the  sulphide  of  the  latter  metal  is  liable  to  be  contaminated 
with  traces  of  oxysulphide.  Such  an  impurity  would  bring  the  atomic 
weight  out  too  high.  The  results  of  two  different  processes,  one  carried 
out  by  himself  and  the  other  in  his  laboratory  by  Rawack,  are  given  by 
Schneider  in  this  paper. 

Rawack  reduced  manganoso-manganic  oxide  to  manganous  oxide  by 
ignition  in  a  stream  of  hydrogen,  and  weighed  the  water  thus  formed. 
From  his  weighings  I  get  the  values  in  the  third  column,  which  repre- 
sent the  Mn304  equivalent  to  one  gramme  of  water: 

4.149  grm.  Mn3O4  gave  0.330  grm.  II2O.  12.5727 

4.649  "  .370          "  12.5643 

6.8865  .5485        "  12.5552 

7.356  "  .5855        "  12.5636 

8-9445  -7135        "  12.5361 

11.584  .9225        "  12.5572 

Mean,  12.5582,  ±.0034 

Here  the  most  obvious  source  of  error  lies  in  the  possible  loss  of  water. 
Such  a  loss,  however,  would  increase  the  apparent  atomic  weight  of 
manganese ;  but  we  see  that  the  value  found  is  much  lower  than  that^ 
obtained  either  by  Dumas  or  von  Hauer. 

Schneider  himself  effected  the  combustion  of  manganous  oxalate  with 
oxide  of  copper.  The  salt  was  not  absolutely  dry,  so  that  it  was  neces- 
sary to  collect  both  water  and  carbon  dioxide.  Then,  upon  deducting 
the  weight  of  water  from  that  of  the  original  material,  the  weight  of 
anhydrous  oxalate  was  easily  ascertained.  Subtracting  from  this  the 
CO?,  we  get  the  weight  of  Mn.  If  we  put  CO2  =  100,  the  quantities  of 
manganese  equivalent  to  it  will  be  found  in  the  last  column : 

1.5075  grm.  oxalate  gave  .306  grm.  H2O  and   .7445  grm.  CO2.  61.3835 

2.253  .4555  "  *-ll35         "  61.4291 

3.1935  -652  1-5745         "  61.4163 

5.073  "  1.028  ."  2.507  "  61.3482 


Mean,  61.3943,  =b  .0122 

Up  to  this  point  the  data  give  two  distinct  values  for  Mn — one  near 
54,  the  other  approximately  55 — and  with  no  sure  guide  to  preference 
between  them.  The  higher  value,  however,  has  been  confirmed  by  later 
testimony. 

In  1883  Dewar  and  Scott  f  published  the  results  of  their  work  upon 
silver  permanganate.  This  salt  is  easily  obtained  pure  by  recry  stall  iza- 
tion,  and  has  the  decided  advantage  of  not  being  hygroscopic.  Two  sets 

*  Poggend.  Annalen,  107,  605. 
tProc.  Roy.  Soc.,  35,  44.     1883. 


284  THE    ATOMIC    WEIGHTS. 

of  experiments  were  made.  First,  the  silver  permanganate  was  heated 
to  redness  in  a  glass  hulb,  first  in  air,  then  in  hydrogen.  Before  weigh- 
ing, the  latter  gas  was  replaced  by  nitrogen.  The  data  are  as  follows  : 


^g  +  MnO.  Per  cent.  Ag  +  MnO. 

5-8696                               4.63212  78.917 

5-4988                               4-33591  78.852 

7.6735                               6.05395  78.894 

13-10147                            10.31815  78.756 

12.5799                          {9.9.065  78.782 

(9.91435      ,  78.811 


Mean,  78.835,  ±  .0174 

The  duplication  of  the  last  weighing  is  not  explained. 

In  the  second  series  the  permanganate  was  dissolved  in  dilute  nitric 
acid,  reduced  by  sulphur  dioxide,  potassium  nitrite,  or  sodium  formate, 
and  titrated  with  potassium  bromide.  The  AgMn04  equivalent  to  100 
KBr  appears  in  the  third  column. 

AgMnO±.  KBr.  Ratio. 

6.5289  3-42385  190.686 

7.5378  3-9553  190.575 

6.1008  3.20166  *  90.559 

5.74647  3-00677  191.117 

6.16593  3. 23602  190.540 

5.11329  2.6828  190.596 

5.07438  2.66204  190.624 

13.4484  7.05602  190.604 

12.5799  6.60065  190.588 

12.27025  6.43808  190.584 

Mean,  190.647,  ±  .0361 

Vacuum  weights  are  given  throughout.  To  the  first  series  of  experi- 
ments the  authors  attach  little  importance,  and  numbers  1  and  4  of  the 
second  series  they  also  regard  as  questionable.  These  experiments  rep- 
resent the  use  of  sulphur  dioxide  as  the  reducing  agent,  and  were  attended 
by  the  formation  of  an  insoluble  residue,  apparently  of  a  sulphide.  Ex- 
cluding them,  the  remaining  eight  experiments  of  the  second  series  give 
in  mean  — 

KBr  :  AgMnO4  :  :  100  :  190.584,  db  .0062, 

which  will  be  used  for  the  present  calculation.  Dewar  and  Scott  also 
made  determinations  with  manganese  chloride  and  bromide.  With  the 
first  salt  they  found  Mn  =  54.91,  and  with  the  second,  Mn  =  54.97  ;  but 
they  give  no  details. 

Marignac's  work  upon  the  atomic  weight  of  manganese  also  appeared 
in  1883.*  He  prepared  the  oxid.e,  MnO,  by  ignition  of  the  oxalate  and 


^Arch.  vSci.  Phys.  et  Nat.  (3),  10.  21.     1883. 


MANGANESE.  285 

subsequent  reduction  of  the  resulting  Mn3O4  in  hydrogen.  The  oxide, 
with  various  precautions,  was  then  converted  into  sulphate.  The  per- 
centage of  MnO  in  MnS04  is  appended  : 

2.6587  grrn.  MnO  gave  5.6530  MnSO4.  47.032  per  cent. 

2.5185  "               5-3600       "  46.987       " 

2.5992  5-5295       "  47.oo6       " 

2.8883  6.1450       "  47.002       " 

Mean,  47.007,  +  .0025 

J.  M.  Weeren,  in  1890,*  published  determinations  made  by  two  meth- 
ods, the  one  Marignac's,  the  other  von  Hauer's.  From  manganese  sul- 
phate he  threw  down  the  hydrated  peroxide  electrolytically,and  the  latter 
compound  was  then  reduced  in  hydrogen  which  had  been  proved  to  be 
free  from  oxygen.  The  resulting  monoxide  was  cooled  in  a  stream  of 
purified  nitrogen.  After  the  oxide  had  been  treated  with  sulphuric  acid, 
converted  into  sulphate,  and  weighed,  a  few  drops  of  sulphuric  acid  and 
a  little  sulphurous  acid  were  added  to  it,  after  which  it  was  reheated  and 
weighed  again.  This  process  was  repeated  until  four  successive  weigh- 
ings absolutely  agreed.  The  results  of  this  set  of  experiments  were  as 
follows,  with  vacuum  standards : 

15.2349  grm.  MnO  gave  32.4142  MnSO4.  47.005  per  cent. 

13.9686  "  29.7186       "  47.004        " 

13.7471  »  29.2493       "  47.000        "       ^ 

15.5222  "  33.0246       "  47.001        " 

14.9824  "  3I-8755       "  47.002       " 

14.6784  "  3 » -2304      "  47.000 

Meanj  47.002,  ±  .0006 

Marignac's  mean,  combined  with  this,  hardly  affects  either  the  per- 
centage itself  or  its  probable  error.  Fortunately,  both  Marignac  and 
Weeren  are  completely  in  agreement  as  to  the  ratio,  and  either  set  of 
measurements  would  be  valid  without  the  other.  In  order,  therefore,  to 
give  Marignac's  work  some  proper  recognition,  we  can  assume  a  general 
mean  of  47.004,  =b  .0006,  without  danger  of  serious  error. 

The  manganese  sulphate  produced  in  the  foregoing  series  of  experi- 
ments was  used,  with  many  precautions,  for  the  next  series  carried  out 
by  von  Hauer's  method.  It  was  transferred  to  a  porcelain  boat,  dried  at 
260°  to  avoid  errors  due  to  retention  of  water  taken  up  in  the  process  of 
transfer,  and  then  heated  to  constant  weight  in  a  stream  of  hydrogen 
sulphide.  Before  weighing,  the  sulphide  was  heated  to  redness  in  hy- 
drogen and  cooled  in  the  same  gas.  The  results,  with  vacuum  weights, 
were  as  follows  : 

*  Atom-Gewichtsbestimmung  des  Mangans.     Inaugural  Dissertation,  Halle,  1890. 


286  THE    ATOMIC    WEIGHTS. 

16.0029  grm-  MnSO4  gave  9.2228  MnS  —  57.632  per  cent. 
16.3191  "  9.4048     "  57.631 

15.9307  9.1817     "  57-634       " 

15-8441  9-131$     "  57.634       " 

16.2783  9.3819     "  57.635       " 

17.0874  9-8477     "  57.633       " 

Mean,  57.633,  ±  .0004 
von  Hauer  found,  57.608,  =b  .0080 

Hence  the  general  mean  is  identical  with  Weeren's  to  the  third  deci- 
mal place,  which  is  unaffected  by  combination  with  von  Hauer's  data. 
We  have  now  to  consider  the  following  ratios  for  manganese : 

(i.)  2AgCl  :  MnCl2  :  :  100  :  41.924,  =b  .0150 

(2.)   2Ag  :  MnCl2  :  :  loo  :  58.321,  d=  .0010 

(3.)    1J2O  :  Mn3O4  :  :  100  :  1255.82,  ±  .340 

(4. )   2L'O2  :  Mn  :  :  100  :  61.3943,  ±  .0122 

(5.)   AgMnO4  :  Ag  -f  MnO  :  :  100  :  78.835,  ±  .0174 

(6.)  KBr  :  AgMnO4  :  :  100  :  190.584,  ±  .0062 

(7.)   MnSO4  :  MnO  :  :  100  :  47.004,  ±  .0006 

(8.)   MnSO4  :  MnS  :  :  100  :  57.633,  ±  .0004 

Computing  with  the  subjoined  preliminary  data — 

O   —    15.879,^.0003  K      =   38.817,^.0051 

Ag  =  107.108,  ±  .0031  C    =  1 1.920,  ±  .0004 

Cl  =  35.179,  dr  .0048          S    —  31.828,^.0015 
Br  =  79-344,  ±  .0062         AgCl  =  142.287,  ±  -0037 

these  ratios  reduce  as  follows  : 

First,  for  the  molecular  weight  of  manganese  chloride,  two  values  are 
deducible. 

From  (i) MnCl2  —  124.996,  d=  .0428 

From  (2) "        =  124.933,  ±  .0042 

General  mean MnO2  — •  124.934,  ±  .0042 

Hence  Mn  =  54.576,  ±  .0075. 

For  manganese  there  are  seven  independent  values,  as  follows  : 

From  molecular  weight  MnCl2 Mn  =  54.576,  ±  .0075 

From  (3) "   =  5.3.667,  ±..0203 

From  (4) "   =  53.633,  ±  .0107 

From  (5) "   =  54.450,  ±  .1511 

From  (6) "   =  54.572,  ±  .0173 

From  (7) "   —  54.601,  ±  .0018 

From  (8) "   =  54-575,  dr  .0022 

General  mean Mn  =  54.571,  =fc  .0013 

If  0  =  16,  this  becomes  Mn  =  54.987. 

In  this  case  five  of  the  separate  values  are  well  in  accord,  and  the  re- 
jection of  the  two  aberrant  values,  which  have  high  probable  errors,  is 


IRON.  287 

not  necessary.  Their  influence  is  imperceptible.  Weeren's  marvelously- 
concordant  data  seem  to  receive  undue  weight,  but  they  are  abundantly 
confirmed  by  the  evidence  of  other  experimenters.  In  short,  the  atomic 
weight  of  manganese  appears  to  be  quite  well  determined. 


IRON. 

The  atomic  weight  of  iron  has  been  mainly  determined  from  the  com- 
position of  ferric  oxide,  with  some  rather  scanty  data  relative  to  other 
compounds. 

Most  of  the  earlier  data  relative  to  the  percentage  of  metal  and  oxygen 
in  ferric  oxide  we  may  reject  at  once,  as  set  aside  by  later  investigations. 
Among  this  no  longer  valuable  material  there  is  a  series  of  experiments 
by  Berzelius,  another  by  Dobereiner,  and  a  third  by  Capitaine.  The 
work  done  by  Stromeyer  and  by  Wackenroder  was  probably  good,  but 
I  am  unable  to  find  its  details.  The  former  found  30.15  per  cent,  of 
oxygen  in  the  oxide  under  consideration,  while  Wackenroder  obtained 
figures  ranging  from  a  minimum  of  30.01  to  a  maximum  of  30.38  per 
cent.* 

In  1844  Berzelius  f  published  two  determinations  of  the  ratio  in  ques- 
tion. He  oxidized  iron  by  means  of  nitric  acid,  and  weighed  the  oxide 
thus  formed.  He  thus  found  that  when  0  =  100  Fe  —  350.27  and 
350.369. 

Hence  the  following  percentages  of  Fe  in  Fe203 : 

70.018 
70.022 


Mean,  70.020,  ±  .0013 

About  the  same  time  Svanberg  and  Norlin  {  published  two  elaborate 
series  of  experiments ;  one  relating  to  the  synthesis  of  ferric  oxide,  the 
other  to  its  reduction.  In  the  first  set  pure  piano-forte  wire  was  oxidized 
by  nitric  acid,  and  the  amount  of  oxide  thus  formed  was  determined. 
The  results  were  as  follows : 


1.5257  grm. 

Fe  gave  2.1803 

grm.  Fe2Os. 

69.977  per  cent.  Fe. 

2.4051 

3-4390 

" 

69.936 

it 

2.3212 

3-3r94 

it 

69.928 

(( 

2.32175 

3.3»83 

" 

,       69.968 

a 

2.2772 

3.2550 

(t 

69.960 

" 

2.4782 

3.5418 

" 

69.970 

" 

2.3582 

3.3720 

<  < 

69.935 

"               , 

Mean,  69.9534, 

±  .0050 

*  For  additional  details  concerning  these  earlier  papers  I   must  refer  to  Oudemans'  mono- 
graph, pp.  140,  141. 

t  Ann.  Chem.  Pharm.,  30,  432.     Berz.  Jahresb.,  25,  43. 
I  Berzelius'  Jahresbericht,  25,  42. 


288  THE    ATOMIC    WEIGHTS. 

Iii  the  second  series  ferric  oxide  was  reduced  by  ignition  in  a  current 
of  hydrogen,  yielding  the  subjoined  percentages  of  metal : 

2.98353  grm.  Fe2O3  gave  2.08915  grm.  Fe.  70.025  per  cent. 

2.41515  i.6oro  70.015        " 

299175  "  2.09455        "  70.014       " 

3.5783  2.505925      »  70.030       " 

4.1922  2.9375  70.072       " 

3.1015  "  2.17275        "  70.056       " 

2.6886  "  1.88305        "  70.036       " 


Mean,  70.0354,  ±  .0055 

It  is  evident  that  one  or  both  of  these  series  must  be  vitiated  by  con- 
stant errors,  and  that  these  probably  arise  from  impurities  in  the  mate- 
rials employed.  Impurities  in  the  wire  taken  for  the  oxidation  series 
could  hardly  have  been  altogether  avoided,  and  in  the  reduction  series 
it  is  possible  that  weighable  traces  of  hydrogen  may  have  been  retained 
by  the  iron.  At  all  events,  it  is  probable  that  the  errors  of  both  series 
are  in  contrary  directions,  and  therefore  in  some  measure  compensatory. 

In  1844  there  was  also  published  an  important  paper  by  Erdmann 
and  Marchand.*  These  chemists  prepared  ferric  oxide  by  the  ignition 
of  pure  ferrous  oxalate,  and  submitted  it  to  reduction  in  a  stream  of 
hydrogen.  Two  sets  of  results  were  obtained  with  two  different  samples 
of  ferrous  oxalate,  prepared  by  two  different  methods.  For  present  pur- 
poses, however,  it  is  not  necessary  to  discuss  these  sets  separately.  The 
percentages  of  iron  in  Fe203  are  as  follows : 

70.013  ] 
69.962    | 

69.979     }-A. 

70.030  I 

69.977  J 

70.044  1 

70.015  j-B. 

70.055  J 

Mean,  70.0094,  =b  .0080 

In  1850  Maumene'sf  results  appeared.  He  dissolved  pure  iron  wire 
in  aqua  regia,  precipitated  with  ammonia,  filtered  off  the  precipitate, 
washed  thoroughly,  ignited,  and  weighed,  after  the  usual  methods  of 
quantitative  analysis.  The  percentages  of  Fe  in  Fe203  are  given  in  the 
third  column : 

1.482  grm.  Fe  gave  2.117  grm.  Fe2O3.  70.005  per  cent. 

1.452  2.074     "  70.010   " 

1.3585     "      1.941     "  69.990 

1.420     "      2.0285    "  70.002   " 

1.492  2.1315    "  69.998   " 

1-554  "  2.22O  "  7O.OOO          " 


Mean,  70.0008,  =h  .0019 


*  Journ.  fiir  Prakt.  Chem.,  33,  i.     1844. 
tCompt.  Rend.,  Oct.  17,  1850. 


IRON.  289 

Two  more  results,  obtained  by  Rivot*  through  the  reduction  of  ferric 
oxide  in  hydrogen,  remain  to  be  noticed.     The  percentages  are : 

69.31 
69-35 

Mean,  69.33,  ±  .013 

We  have  thus  before  us  six  series  of  results,  which  we  may  now  com- 
bine : 

Berzelius 70.020,    ±  .0013 

Erdmann  and  Marchand 70.0094,  =b  .0080 

Svanberg  and  Norlin,  oxidation 69.9534,  ±  .0050 

Svanberg  and  Norlin,  reduction 70.0354,  ±  .0055 

Maumene 70.0008,  ±  .0019 

Rivot 69.33,      ±  -OI3 


General  mean 70.0075,  ±  .0010 

From  this  we  get  Fe  =  55.596. 

Dumas'  f  results,  obtained  from  the  chlorides  of  iron,  are  of  so  little 
weight  that  they  might  safely  be  omitted  from  our  present  discussion. 
For  the  sake  of  completeness,  however,  they  must  be  included. 

Pure  ferrous  chloride,  ignited  in  a  stream  of  hydrochloric  acid  gas, 
was  dissolved  in  water  and  titrated  with  a  silver  solution  in  the  usual 
way.  One  hundred  parts  of  silver  are  equivalent  to  the  amounts  of  Fed, 
given  in  the  third  column  : 

3.677  grm.  FeCl.2  =  6.238  grm.  Ag.  58.945 

3.924  "          =6.675         "  58.787 

Mean,  58.866,  ±  .053 

Ferric  chloride,  titrated  in  the  same  way,  gave  these  results : 

1.179  grm-  FeCl3  =  2.3475  grm.  Ag.  50.224 

1.242  "  =2.471  "  5°-263 

Mean,  60.2435,  ±  .0132 

These  give  us  two  additional  values  for  Fe,  as  follows : 

From  FeC!2 Fe  =  55.742 

From  FeCls "  =  55.907 

A  series  of  determinations  of  the  equivalent  of  iron,  made  by  students 
by  measuring  the  hydrogen  evolved  when  the  metal  is  dissolved  in  an 
acid,  was  published  by  Torrey  in  1888. J  The  data  have,  of  course,  slight 

*  Ann.  Chem.  Pharm.,  78,  214.  1851. 
f  Ann.  Chem.  Pharm.,  113,  26.  1860. 
I  Am.  Chem.  Journ.,  10,  74. 

19 


290  THE    ATOMIC   WEIGHTS. 

value,  but  may  be  considered  as  being  in  some  measure  confirmatory. 

They  are  as  follows  : 

56.40 

55.6o 
55-3* 
55.56 
55.48 

55-5° 
55.86 
56.06 
56.22 
55-So 
55-78 
55.6o 
55.70 
55-94 


Mean,  55-777,  ±  .0532 

These  values  undoubtedly  depend  on  Regnault's  value  for  the  weight 
of  hydrogen.  Correcting  by  the  later  value,  as  found  in  the  chapter  of 
this  work  relating  to  the  density  ratio  H  :  0,  the  mean  becomes  Fe  = 
55.608,  zh  .0532.  Here  the  probable  error  in  the  weight  of  the  hydrogen 
is  ignored,  as  being  of  no  practical  significance. 

The  four  ratios  for  iron  are  now  as  follows  : 

(i.)  Per  cent.  Fe  in  Fe2O3,  70.0075,  ±  .0010 

(2.)  Ag2  :  FeG2  :  :  loo  :  58.866,  ±  .0530 

(3.)  Ag3  :  FeC)3  :  :  100  :  50.2435,  ±  .0132 

(4.)  H:Fe::  I  :  55.608,^.0532 

Reducing  these  with  — 

O   =   15.879,  ±  .0003 

Ag  =  107.108,  ±  .0031 

Cl  •=    35.179,  ±  .0048 


we  have — 


From  (i) Fe  =  55.596,  ±  .0023 

From  (2) "  =  55.742,  ±  .1140 

From  (3) "  =  55.907,  ±  .0450 

From  (4) "  =  55.608,  =b  .0532 


General  mean Fe  =  55.597,  ±  .0023 

If  O  =  16,  then  Fe  =  56.021.     Here  all  the  values  are  absorbed  prac- 
tically by  the  first,  the  other  three  having  no  real  significance. 


NICKEL    AND    COBALT.  291 


NICKEL  AND  COBALT. 

On  account  of  the  close  similarity  of  these  metals  to  each  other,  their 
atomic  weights,  approximately  if  not  actually  identical,  have  received 
of  late  years  much  attention. 

The  first  determinations,  and  the  only  ones  up  to  1852,  were  made  by 
Rothhoff,*  each  with  but  a  single  experiment.  For  nickel  188  parts  of 
the  monoxide  were  dissolved  in  hydrochloric  acid ;  the  solution  was 
evaporated  to  dryness,  the  residue  was  dissolved  in  water,  and  precipi- 
tated by  silver  nitrate.  718.2  parts  of  silver  chloride  were  thus  formed  ; 
whence  Ni  =  58.613.  The  same  process  was  applied  also  to  cobalt,  269.2 
parts  of  the  oxide  being  found  equivalent  to  1029.9  of  AgCl ;  hence  Co  = 
58.504.  These  values  are  so  nearly  equal  that  their  differences  were 
naturally  ascribable  to  experimental  errors.  They  are,  however,  entitled 
to  no  special  weight  at  present,  since  it  cannot  be  certain  from  any  evi- 
dence recorded  that  the  oxide  of  either  metal  was  absolutely  free  from 
traces  of  the  other. 

In  1852  Erdmann  and  Marchand  f  published  some  results,  but  with- 
out details,  concerning  the  atomic  weight  of  nickel.  They  reduced  the 
oxide  by  heating  in  a  current  of  hydrogen,  and  obtained  values  ranging 
from  58.2  to  58.6,  when  0  =  16.  Their  results  were  not  very  concordant, 
and  the  lowest  was  probably  the  best. 

In  1856,  incidentally  to  other  work,  Deville  J  found  that  100  parts  of 
pure  metallic  nickel  yielded  262  of  sulphate ;  whence  Ni  =  58.854. 

To  none  of  the  foregoing  estimations  can  any  importance  now  be  at- 
tached. The  modern  discussion  of  the  atomic  weights  under  considera- 
tion began  with  the  researches  of  Schneider  §  in  1857.  This  chemist 
examined  the  oxalates  of  both  metals,  determining  carbon  by  the  com- 
bustion of  the  salts  with  copper  oxide  in  a  stream  of  dry  air.  The  carbon 
dioxide  thus  formed  was  collected  as  usual  in  a  potash  bulb,  which,  in 
weighing,  was  counterpoised  by  a  similar.bulb,  so  as  to  eliminate  errors 
due  to  the  hygroscopic  character  of  the  glass.  The  metal  in  each  oxalate 
was  estimated,  first  by  ignition  in  a  stream  of  dry  air,  followed  by  intense 
heating  in  hydrogen.  Pure  nickel  or  cobalt  was  left  behind  in  good  con- 
dition for  weighing.  Four  analyses  of  each  oxalate  were  made,  with  the 
results  given  below.  The  nickel  salt  contained  three  molecules  of  water, 
and  the  cobalt  salt  two  molecules  : 

*  Cited  by  Berzelius.     Poggend.  Annaleti,  8,  184.    1826. 
t  Journ.  fiir  Prakt.  Chem.,  55,  202.     1852. 
t  Ann.  Chim.  Phys.  (3),  46,  182.     1856. 
t Poggend.  Annalen,  101,  387.     1857. 


292  THE    ATOMIC    WEIGHTS. 


1.1945  grm.  gave    .528   grm.  CO2.  44.203  per  cent. 

2.5555         "  1.12625       "  44-072       " 

3.199  "          1.408  44.014       " 

5.020  "          2.214  44.104       " 

Mean,  44.098,  ±  .027 

The  following  percentages  of  nickel  were  found  in  this  salt 

29.107 
29.082 
29.066 
29.082 


Mean,  29.084,  dz  .006 


rm.  gave    .781    grm.  CO2.  47-753  Per  cent. 

1.107  "  .5295          "  47-832       " 

2.309  "          i.ioi  47-683       " 

3.007  1-435  47.722       " 

Mean,  47-7475,  ±  .0213 

The  following  were  the  percentages  found  for  cobalt : 

32-552 
32.619 
32.528 
32.523 


Mean,  32.5555,  ±  .0149 

In  a  later  paper*  Schneider  also  gives  some  results  obtained  with  a 
nickel  oxalate  containing  but  two  molecules  of  water.  This  gave  him 
47.605  per  cent,  of  C02,  and  the  following  percentages  of  nickel : 

3I-4"5 
31-4038 


Mean,  31.4076,  d=  .0026 

The  conclusion  at  which  Schneider  arrived  was  that  the  atomic  weights 
of  cobalt  and  nickel  are  not  identical,  being  about  60  and  58  respectively. 
The  percentages  given  above  will  be  discussed  at  the  end  of  this  chapter 
in  connection  with  all  the  other  data  relative  to  the  constants  in  ques- 
tion. 

The  next  chemist  to  take  up  the  discussion  of  these  atomic  weights 
was  Marignac,  in  1858.f  He  worked  with  the  chlorides  and  sulphates 

*Poggend.  Annalen,  107,  616. 

t  Arch,  des  Sci.  Phys  et  Nat.  (nouv.  serie),  i,  372.     1858. 


NICKEL    AND    COBALT.  293 

of  nickel  and  cobalt,  using  various  methods,  but  publishing  few  details, 
as  he  did  not  consider  the  determinations  final.  The  sulphates,  taken 
as  anhydrous,  were  calcined  to  oxides.  From  the  ratio  NiS04  :  NiO,  he 
found  Ni  =  58.4  to  59.0,  and  from  five  measurements  of  the  ratio 
CoS04 :  Co,  Co  =  58.64  to  58.76.  If  oxygen  is  taken  as  16,  these  give  for 
the  percentages  of  oxide  in  sulphate  : 

CoO  in  CoSOv  NiO  in 

48.267  48.187 

48.307  48.387 


Mean,  48.287,  d=  .0135  Mean,  48.287,  ±  .0675 

The  chlorides  were  dried  at  100°,  but  found  to  retain  water;  and  in 
most  cases  were  then  either  fused  in  a  stream  of  chlorine  or  of  dry, 
gaseous  hydrochloric  acid,  or  else  calcined  gently  with  ammonium 
chloride.  The  determinations  were  then  made  by  titration  with  a 
standard  solution  of  silver  in  nitric  acid.  Three  experiments  with  an- 
hydrous CoCl,  gave  Co  =  58.72  to  58.84.  Three  more  with  CoCl2  dried 
at  100°  gave  Co  =  58.84  to  59.02.  Three  with  anhydrous  NiCl2  gave 
Ni  =  58.80  to  59.00.  If  the  calculations  were  made  with  Ag  =  108  and 
Cl  =  35.5,  then  these  data  give  as  proportional  to  100  parts  of  silver : 


60.093 
60.185 

Mean,  60.139,  ±  .0310 
,  Mean,  60.118,  ±  .0192 

In  one  more  experiment  NiCl.2  was  precipitated  with  a  known  quan- 
tity of  silver.  The  filtrate  was  calcined,  yielding  NiO  ;  hence  the  ratio 
,Ag-2 :  NiO,  giving  Ni  =  59.29.  This  experiment  needs  no  farther  atten- 
tion. 

In  short,  according  to  Marignac,  and  contrary  to  Schneider's  views, 
the  two  atomic  weights  are  approximately  the  same.  Marignac  criticises 
Schneider's  earlier  paper,  holding  that  the  nickel  oxalate  may  have  con- 
•tained  some  free  oxalic  acid,  and  that  the  cobalt  salt  was  possibly  con- 
taminated with  carbonate  or  with  basic  compounds.  In  his  later  papers 
Schneider  rejects  these  suggestions  as  unfounded,  and  in  turn  criticises 
Marignac.  The  purity  of  anhydrous  NiS04  is  not  easy  to  guarantee,  and, 
according  to  Schneider,  the  anhydrous  chlorides  of  cobalt  and  nickel  are 
liable  to  be  contaminated  with  oxides.  This  is  the  case  even  when  the 
chlorides  are  heated  in  chlorine,  unless  the  gas  is  carefully  freed  from 
all  traces  of  air  and  moisture. 


294 


THE    ATOMIC    WEIGHTS. 


Dumas'  *  determinations  of  the  two  atomic  weights  were  made  with 
the  chlorides  of  nickel  and  cobalt.  The  pure  metals  were  dissolved  in 
aqua  regia,  the  solutions  were  repeatedly  evaporated  to  dryness,  and  the 
residual  chlorides  were  ignited  in  dry  hydrochloric  acid  gas.  The  last 
two  estimations  in  the  nickel  series  were  made  upon  NiCL2  formed  by 
heating  the  spongy  metal  in  pure  chlorine.  In  the  third  column  I  give 
the  NiCl2  or  CoCl2  equivalent  to  100  parts  of  silver : 

.9123  grm.  NiCl2  =  1.515  grm.  Ag.  60.218 

2.295  "  3-8ii5       "  60.212 

3.290  5.464         "  60.212 

1.830  "  3.041          "  60.178 

3.001  "  4.987         "  60.176 


Mean,  60.1992,  ±  .0062 


2  352  grm.  CoCl2  =  3.9035  grm.  Ag.  60.254 

4.210  6.990         "  60.229 

3.592  "  5.960         "  60.268 

2.492  "  4.1405       "  60.186 

4.2295  "  7.0255        "  60.202 


Mean,  60.2278,  ±  .on 

These  results  give  values  for  Co  and  Ni  differing  by  less  than  a  tenth 
of  a  unit ;  here,  as  elsewhere,  the  figure  for  Ni  being  a  trifle  the  lower. 
Combining  these  data  with  Marignac's,  we  have — 

Agi  :  NiC^  :  :  100  :  x. 

Marignac 60. 139,  ±  .0310 

Dumas 60.199,^.0062 


General  mean    60. 194,  db  .0061 

Ag^  :  CoCl2  :  :  TOO  :  X, 

Marignac 60.118,  ±  .0192 

Dumas 60  228,  ±  .0110 


General  mean 60.200,  dr  .0095 

In  1863  f  the  idea  that  nickel  and  cobalt  have  equal  atomic  weights 
was  strengthened  by  the  researches  of  Russell.  He  found  that  the  black 
oxide  of  cobalt,  by  intense  heating  in  an  atmosphere  of  carbon  dioxide, 
became  converted  into  a  brown  monoxide  of  constant  composition.  The 
ordinary  oxide  of  nickel,  on  the  other  hand,  was  shown  to  be  convert- 
ible into  a  definite  monoxide  by  simple  heating  over  the  blast  lamp. 
The  pure  oxides  of  the  two  metals,  thus  obtained,  were  reduced  by 
ignition  in  hydrogen,  and  their  exact  composition  thus  ascertained. 

*Ann.  Chem.  Pharm.,  113,  25.     1860. 
f  Journ.  Chem.  Soc.  (2),  i,  51.     1863. 


NICKEL   AND    COBALT. 


295 


Several  samples  of  each  oxide  were  taken,  yielding  the  following  data. 
The  separate  samples  are  indicated  by  lettering : 

Nickel 


c. 


D. 


B. 


CoO. 

2. 1211 

2.0241 

I    2.1226 

I  L9947 

{3.0628 

2.1167 

I.77I7 

1.7852 
1.6878 
2.2076 
|  2.6851 

(2.1, 


46I 
f  3.4038 

E.  J  2.2778 
(2.1837 


Ni. 

1.6364 

.6468 

•5838 

•  7342 

•  7952 
.6761 

.79" 
.6845 
.9030 

.7179 

•  5788 

1.6379 
2.0873 


Cobalt. 

Co. 
1.6670 

L5907 
1.6673 

1.5678 

2.4078' 

.6638 

.3924 
.4030 

.3264 

•735° 
2.1104 
1.6868 
2.6752 

i.7901 
1.7163 


Percent.  Ni. 

78.597 
78.584 
78.608 
78.581 
78.589 
78.583 
78.616 
78.590 
78.588 
78.590 
78.594 
78.597 
78.588 


Mean,  78.593,  ±  .0018 


Percent.  Co. 

78.591 
78.588 

78.550 
78.598 
78.614 
78.603 
78.591 
78.591 
78.588 
78.592 
78.597 
78.598 
78.595 
78.589 
78.596 


Mean,  78.592,  ±  .0023 


These  percentages  are  practically  identical,  and  lead  to  essentially  the 
same  mean  value  for  each  atomic  weight. 

In  a  later  paper  Russell*  confirmed  the  foregoing  results  by  a  different 
process.  He  dissolved  metallic  nickel  and  cobalt  in  hydrochloric  acid 
and  measured  the  hydrogen  evolved.  Thus  the  ratio  between  the  metal 
and  the  ultimate  standard  was  fixed  without  the  intervention  of  any 
other  element.  About  two-tenths  of  a  gramme  of  metal,  or  less,  was 


*  Journ.  Chem.  Soc.  (2),  7,  494.     1867. 


296 


THE    ATOMIC    WEIGHTS. 


taken  in  each  experiment.  The  data  obtained  were  as  follows ;  the  last 
column  giving  the  weight  of  hydrogen,  computed  from  its  volume, 
yielded  by  100  parts  of  cobalt  or  nickel : 


Wt.  Ni. 
f  .0906 
.1017 
.1990 
A.  <{  .0997 
.1891 

.1859 

.1838 


B.  -  .1806 

.2026 

C.  .1933 
.1890 

D.  -j  .1942 

.1781 


Nickel. 

Vol.  H  in  cc. 

153-62 
172.32 
337.o6 
168.93 
319.86 

314.75 
311-25 

318.75 
305.28 

333-81 
325.93 
319.77 
328.15 
301.09 


Cobalt. 

Vol.  H  in  cc. 
321.36 
312.95 
319-63 
328.96 

328.43 
329.55 
290.17 

308.97 
318.60 

3H.73 
305-4o 


Ratio. 
3.420 
3.418 
3-4i6 

3.417 
3.412 

3.415 
3.4i6 

3.398 
3-409 
3-404 
3.401 

3-412 
3.408 
3-410 

Mean,  3.411,  ±  .001 


Ratio. 

3-395 
3.398 
3-397 
3-398 
3403 
3-401 
3-401 
3-404 
3.405 
3.410 
3.407 


Mean,  3.4017,  ±  .0009 


The  weight  of  the  hydrogen  in  these  determinations  was  doubtless 
computed  from  Regnault's  data  concerning  the  density  of  that  gas.  Cor- 
recting by  the  new  value  for  the  weight  of  a  litre  of  hydrogen,  .089872 
gramme,  the  ratios  become: 

For  nickel   3-42H,  ±  .0010 

For  cobalt 3.4112,  =b  .0009 

Some  time  after  the  publication  of  Russell's  first  paper,  but  before  the 
appearance  of  his  second,  some  other  investigations  were  made  known. 


NICKEL    AND    COBALT.  297 

Of  these  the  first  was  by  Sommaruga,*  whose  results,  obtained  by  novel 
methods,  closely  confirmed  those  of  Schneider  and  antagonized  those 
of  Dumas,  Marignac,  and  Russell.  The  atomic  weight  of  nickel  Som- 
maruga  deduced  from  analyses  of  the  nickel  potassium  sulphate, 
K2Ni(S04)2.6H20,  which,  dried  at  100°,  has  a  perfectly  definite  compo- 
sition. In  this  salt  the  sulphuric  acid  was  determined  in  the  usual  way 
as  barium  sulphate,  a  process  to  which  there  are  obvious  objections.  In 
the  third  column  are  given  the  quantities  of  the  nickel  salt  proportional 
to  100  parts  of  BaS04 : 

0.9798  grm.  gave  1.0462  grm.  BaSO4.  93-653 

1.0537          "  1.1251          "  93.654 

1.0802          "  LI535          "   '  93-645 

1.1865          "  1.2669          "  93.654 

3.2100          "  3.4277          "  93649 

3.2124          "  3.4303          "  93.648 

Mean,  93.6505,  rt  .001 

For  cobalt  Sommaruga  used  the  purpureocobalt  chloride  of  Gibbs 
and  Genth.  This  salt,  dried  at  110°,  is  anhydrous  and  stable.  Heated 
hotter,  CoCl2  remains.  The  latter,  ignited  in  hydrogen,  yields  metallic 
cobalt.  In  every  experiment  the  preliminary  heating  must  be  carried 
on  cautiously  until  arnmoniacal  fumes  no  longer  appear : 

.6656  grm.  gave  .1588  grm.  Co.  23.858  per  cent. 

1.0918  "  .2600       "  23.814  " 

.9058  "  .2160  "  23.846 

L5895  "  .3785  "  23.813  " 

2.9167  "  .6957  "  23.847  " 

1.8390  «  .4378  "  23.806  " 

2.5010  "  .5968  "  23.808 

Mean,  23.827,  ±  .006 

Further  along  this  series  will  be  combined  with  a  similar  one  by  Lee. 
It  may  here  be  said  that  Sommaruga's  paper  was  quickly  followed  by 
a  critical  essay  from  Schneider,f  endorsing  the  former's  work  and  object- 
ing to  the  results  of  Russell. 

In  1867  still  another  new  process  for  the  estimation  of  these  atomic 
weights  was  put  forward  by  Winkler,  J  who  determined  the  amount  of 
gold  which  pure  metallic  nickel  and  cobalt  could  precipitate  from  a 
neutral  solution  of  sodio-auric  chloride. 

In  order  to  obtain  pure  cobalt  Winkler  prepared  purpureocobalt 
chloride,  which,  having  been  four  or  five  times  recrystallized,  was  ignited 
in  hydrogen.  His  nickel  was  repeatedly  purified  by  precipitation  with 
sodium  hypochlorite.  From  material  thus  obtained  pure  nickel  chloride 

*  Sitzungsb.  Wien.  Akad.,  54,  2  Abth.,  50.     1866. 
1  Poggend.  Annalen,/i30,  310. 
1  Zeit.  Anal.  Chem.,  6,  18.     1867. 


298  THE    ATOMIC    WEIGHTS. 

was  prepared,  which,  after  sublimation  in  dry  chlorine,  was  also  reduced 
by  hydrogen.  One  hundred  parts  of  gold  are  precipitated  by  the  quanti- 
ties of  nickel  and  cobalt  given  in  the  third  columns  respectively.  In  the 
cobalt  series  I  include  one  experiment  by  Weselsky,  which  was  published 
by  him  in  a  paper  presently  to  be  cited : 

.4360  grm.  nickel  precipitated  .9648  grm.  gold.  45.191 

•4367  .9666         "  45.179 

•5189  "  I.I457         "  45-29I 

.6002  "  1.3286         "  45.175 


Mean,  45.209,  ±  .019 

.5890  grm.  cobalt  precipitated  1.3045  grm.  gold.  45.151 

•3 '47                                               .6981          "  45.080 

•  5829                                     1.2913        «  45- HI 

•  Sni                                           1.1312         "  45.182 
.5821                                           1.2848         "  45.307 

•559  "  1.241  "  45.044— Weselsky. 

Mean,  45.151,  ±  .025 

Weselsky 's  paper,*  already  quoted,  relates  only  to  cobalt.  He  ignited 
the  cobalticyanides  of  ammonium  and  of  phenylammonium  in  hydrogen, 
and  from  the  determinations  of  cobalt  thus  made  deduced  its  atomic 
weight.  His  results  are  as  follows  : 

•7575  Srm-  (NH4)6CoaCy12  Save  -l66  Srm-  Co-          21.914  per  cent. 
•  5J43  "  .113         "  21.972       " 


Mean,  21.943,  ±  .029 

.8529  grm.  (C6H8N)6Co2Cy12  gave  .1010  grm.  Co.      11.842  per  cent. 
.6112  "  .0723          "  11.829       " 

.7J4°  .0850         "          11.905       " 

.9420  .1120  "  11.890         " 

Mean,  11.8665,  ±.0124 

Next  in  order  is  the  work  done  by  Lee  f  in  the  laboratory  of  Wolcott 
Gibbs.  Like  Weselsky,  Lee  ignited  certain  cobalticyanides  and  also 
nickelocyanides  in  hydrogen  and  determined  the  residual  metal.  The 
double  cyanides  chosen  were  those  of  strychnia  and  brucia,  salts  of  very 
high  molecular  weight,  in  which  the  percentages  of  metal  are  relatively 
low.  A  series  of  experiments  with  purpureocobalt  chloride  was  also 
carried  out.  In  order  to  avoid  admixture  of  carbon  in  the  metallic  resi- 
dues, the  salts  were  first  ignited  in  air,  and  then  in  oxygen.  Reduction 
by  hydrogen  followed.  The  salts  were  in  each  case  covered  by  a  porous 
septum  of  earthenware,  through  which  the  hydrogen  diffused,  and  which 
served  to  prevent  the  mechanical  carrying  away  of  solid  particles ;  fur- 

*  Ber.  d.  Deutsch.  Chem.  Gesell.,  2,  592.     1868. 
t  Am.  Journ.  Sci.  and  Arts  (3),  2,  44.     1871. 


NICKEL    AND    COBALT.  299 

thermore,  heat  was  applied  from  above.  The  results  attained  were  very 
satisfactory,  and  assign  to  nickel  and  cobalt  atomic  weights  varying  from 
each  other  by  about  a  unit ;  Ni  being  nearly  58,  and  Co  about  59,  when 
O  =  16.  The  exact  figures  will  appear  later.  The  cobalt  results  agree 
remarkably  well  with  those  of  Weselsky.  The  following  are  the  data 
obtained : 

Brucia  nickelocyanide,  Ni.ACyVi(^C^H^N^O^&H6.10H20. 

Salt.  Ni.  Percent.  Ni. 

.3966  .0227                                  5.724 

.5638  .0323                                  5.729 

.4000  .0230                                 5-75° 

.3131  -01795  5-733 

.4412  .0252  5.712 

.4346  .0249  5.729 


Mean,  5.7295,  ±.0034 

Strychnia  nickelocyanide,  Ni9 Cyl2(  C2l H^N2  02\H6.8H2  0. 

Salt.  Ni.                            Per  cent.  AY. 

.5358  .0354  6.607 

.5489  .0363  6.613 

.3551  -0234  '  6.589 

•4495  -0297  6-6°7 

.2530  .0166  6.561 

.1956  .0129  6.595 

Mean,  6.595,  ±  .005 

Brucia  cobalticyanide,  Co2 Cyl2(  C2ZH26N2  0^>6H6.20H2  0. 

Salt.  Co.                            Percent.  Co. 

.4097  .0154  3.759 

•3951  .0147  3-720           \ 

•5456  .0204  3.739 

.4402  .0165  3.748 

.4644  .0174  3-747 

.4027  .0151  3.749 


Mean,  3.7437,  ±  .0036 

Strychnia  cobalticyanide,  Co.2Cyl2(C2lH22N20,\H6.8H.20. 

Salt.  Co.  Percent.  Co. 

.4255  -0195  4.583 

.4025  .0185  4.596 

•3733  .0170  4-554 

-4535  -0207  4.564 

-2753  -0126  4.577 

.1429  -0065  4.549 


Mean,  4.5705,  =b  .005 


300  THE   ATOMIC    WEIGHTS. 

Parpureo-cobalt  chloride,  C 


Salt.  Co.            Percent.  Co. 

•9472  .2233  23.575 

.8903  .2100  23.587 

.6084  .1435  23.586 

.6561  .1547  23.579 

.6988  .1647  23.569 

.7010  .1653  23.581 


Mean,  23.5795,  ±  .0019 
The  last  series  may  be  combined  with  Sommaruga's,  thus  : 

Sommaruga 23.817,    ±  .006 

Lee 23.5795,  ±  .0019 


General  mean 23.6045,  ±  .0018 

Baubigny's  *  determinations  of  the  atomic  weight  of  nickel  are  limited 
to  two  experiments  upon  the  calcination  of  nickel  sulphate,  and  his  data 
are  as  follows : 

6.2605  grm.  NiSO4  gave  3.9225  NiO.  48.279  per  cent. 

4.4935  "  2.1695     "  48.281 


Mean,  48.280 

Zimmermann's  work,  published  after  his  death  by  Krtiss  and  Alibe- 
goff,f  was  based,  like  Russell's,  upon  the  reduction  of  cobalt  and  nickel 
oxides  in  hydrogen.  The  materials  used  were  purified  with  great  care, 
and  the  results  were  as  follows: 


Nickel 

1 

mo. 

Ni, 

Percent.  Ni. 

6.0041 

4.7179 

78.578 

6  4562 

5-0734 

78.582 

8.5960 

6.7552 

78.585 

4.7206 

3.7096 

78.583 

8.2120 

6.4536 

78.587 

9-1349 

7.1787 

78.585 

IO.OI56 

7.8702 

78.579 

4.6482 

•  3.6526 

78.580 

8.9315 

7.0184 

78.580 

10.7144 

8.4196 

78.582 

3.0036 

2.3602 

78.579 

Mean,  78.582,  ±  .0006 

*  Compt.  Rend.,  97,  951.     1883. 
f  Ann.  der  Chem.,  232,  324.     1886. 


NICKEL  AND  COBALT.  301 

Cobalt. 

CoO.  Co.  Per  cent.  Co. 

6.3947  5-0284  78.634 
6.6763  5.2501  78.638 
5.6668  4.4560  78.633 
2.9977  2.3573  78.637 
8.7446  6.8763  78-635 
3.2625  2.5655  78.636 

6.3948  5.0282  78.630 
8.2156  6.4606  78.638 
9.4842  7.458o  78.636 
9.9998  7.8630  78.632 

Mean,  78.635,  ±  .0002 

Shortly  after  the  discovery  of  nickel  carbonyl,  NiC4O4,  Mond,  Langer, 
and  Quincke*made  use  of  it  with  reference  to  the  atomic  weight  of 
nickel.  The  latter  was  purified  by  distillation  as  nickel  carbonyl,  then 
converted  into  oxide,  and  that  was  reduced  by  hydrogen  in  the  usual 
way. 

NiO.  Ni.  Per  cent.  Ni. 

.2414  .1896  78.542 

.3186  .2503  78.562 

.3391  .2663  78.531 

Mean,  78.545,  ±  .0061 

Schutzenberger's  experiments,t  published  in  1892,  were  also  few  in 
number.  First,  nickel  sulphate,  dehydrated  at  440°,  was  calcined  to 
oxide. 

3.505  grm.  NiSO4  gave  1.690  NiO.  48.217  per  cent. 

26008  "  1.2561     "  48.297       " 

Mean,  48.257,  ±  .027 

Second,  nickel  oxide  was  reduced  in  hydrogen,  as  follows : 

1.6865  grm.  NiO  gave  1.3245  Ni.  78.535  per  cent. 

1.2527  "  .9838    "  78.533       " 

Mean,  78.534 

Iii  one  experiment  with  cobalt  oxide,  3.491  grm.  gave  2.757  Co,  or 
78.975  per  cent.  In  view  of  the  many  determinations  of  this  ratio  by 
other  observers,  this  single  estimation  may  be  neglected.  The  experi- 
ments on  nickel  sulphate,  however,  should  be  combined  with  those  of 
Marignac  and  Baubigny,  giving  the  latter  equal  weight  with  Schutzen- 
berger's, thus : 

*Journ.  Chem.  Soc.,  57,  753.     1890. 
tConipt.  Rend.,  114,  1149.     1892. 


302 


THE    ATOMIC    WEIGHTS. 

Marignac 48.287,  ±  .0675 

Baubigny 48.280,  ±  .027 

Schutzenberger 48.257,  ±  .027 


General  mean.  .....    48.269,  ±  .018 

From  this  point  on  the  determination  of  these  atomic  weights  is  com- 
plicated by  the  questions  raised  by  Kriiss  as  to  the  truly  elementary 
character  of  nickel  and  cobalt.  If  that  which  has  been  called  nickel 
really  contains  an  admixture  of  some  other  hitherto  unknown  element, 
then  all  the  determinations  made  so  far  are  worthless,  and  the  investiga- 
tions now  to  be  considered  bear  directly  upon  that  question.  First  in 
order  comes  Remmler's  research  upon  cobalt.*  This  chemist,  asking 
whether  cobalt  is  homogeneous,  prepared  cobaltic  hydroxide  in  large 
quantity,  and  made  a  series  of  successive  ammoniacal  extracts  from  it, 
twenty-five  in  all.  Each  extract  represented  a  fraction,  from  which,  by 
a  long  series  of  operations,  cobalt  monoxide  was  prepared,  and  the  latter 
was  reduced  in  hydrogen  after  the  manner  of  Russell.  The  actual  deter- 
minations began  with  the  second  fraction,  and  the  data  are  subjoined, 
the  number  of  the  fraction  being  given  with  each  experiment : 


CoO. 

Co. 

Percent.  Co. 

2  09938 

.07837 

78.859 

3  i5°2i 

.11814 

78.650 

4  .22062 

.17360 

78.687 

5  390H 

.30681 

78.647 

6  .28820 

.22661 

78.629 

7  343°4 

.26968 

78.615 

8  43703 

.34321 

78.532 

9  9H77 

.71864 

78.560 

10  63256 

.49661 

78.508 

ii  32728 

.25701 

78.529 

12  .38042 

.29899 

78.595 

13  16580 

.13027 

78.571 

14  I.OI6O7 

•79873 

78.610 

15  I-3I63S 

1-03545 

78.661 

16  91945 

.72315 

78.650 

17  53IQo 

.41773 

78.668   , 

18  82381 

.64728 

78.572 

19  81139 

.63754 

78.574 

20  76698 

.60292 

78.610 

21  LI3693 

.89412 

78.643 

22  2.OO259 

1-57495 

78.646 

23  1.04629 

.82185 

78.549 

24  48954 

.38466 

78.576 

25  69152 

.54326 

78.560 

Mean,  78.613,  ±  .0099 

*Zeit.  Anorg.  Chem.,  2,  221.     Also  more  fully  in  an  Inaugural  Dissertation,  E)rlangen, 


NICKEL    AND    COBALT.  303 

Considered  with  reference  to  the  purpose  of  the  investigation,  this 
mean  and  its  probable  error  have  no  real  significance.  But  it  is  very 
close  to  the  means  of  other  experimenters,  and  a  study  of  the  variations 
represented  by  the  several  fractions  seems  to  indicate  fortuity  rather 
than  system.  Remmler  regards  his  results  as  indicating  lack  of  homo- 
geneity in  his  material ;  but  it  seems  more  probable  that  such  differences 
as  exist  are  due  to  experimental  errors  and  to  impurities  acquired  in  the 
long  process  of  purification  to  which  each  fraction  was  submitted,  rather 
than  to  any  uncertainty  regarding  the  nature  of  cobalt  itself.  For  either 
interpretation  the  data  are  inconclusive,  and  I  therefore  feel  justified  in 
treating  the  mean  like  other  means,  and  in  combining  it  finally  with 
them. 

From  the  same  point  of  view — that  is,  with  reference  to  the  supposed 
heterogeneity  of  nickel — Kruss  and  Schmidt  *  carried  out  a  series  of  frac- 
tionations  of  the  metal  by  distillation  in  a  stream  of  carbon  monoxide. 
Nickel  oxide,  free  from  obnoxious  impurities,  was  first  reduced. to  metal 
by  heating  in  hydrogen,  after  which  the  current  of  carbon  monoxide  was 
allowed  to  flow.  The  latter,  carrying  its  small  charge  of  nickel  tetra- 
carbonyl  was  then  passed  through  a  Winkler's  absorption  apparatus  con- 
taining pure  aqua  regia,  from  which,  by  evaporation,  nickel  chloride  was 
obtained,  and  from  that,  by  reduction  in  hydrogen,  the  nickel.  Ten 
such  fractions  were  successively  prepared  and  studied  ;  first,  by  prepa- 
ration of  NiO  and  its  reduction  in  hydrogen  ;  and,  secondly,  in  some 
cases,  by  the  reoxidation  of  the  reduced  metal,  so  as  to  give  a  synthetic 
value  for  the  ratio  Ni :  0.  The  data  obtained  are  as  follows,  the  successive 
fractions  being  numbered  : 

Reduction  of  NiO. 
NiO.  Ni.  Per  cent.  Ni. 


J  1  .3722 

.2926 

78.614 

'  1  .7471 

.5870 

78.571 

2  {  .7659 
•  I  .7606 

.60085 
.5961 

78.450 
78.372 

0.0175 

.7984 

78.467 

3.  -j  1.2631 

.99065 

78.430 

(1.2582 

.9868 

78.429 

4-  -!  '5I93 

.4076 

78.490 

\  .9200 

.7215 

78.424 

f  -4052 

.3179 

78.455 

'*  1  .65J8 

.5111 

78.414 

6  I  *5623 

•4399 

78.232 

'  1  .5556 

•4350 

78.294 

(  -9831 

.7724 

78.568 

7-  -j  .9765 

.7646 

78.300 

(.  -9639 

•  7557 

78.400 

*Zeit.  Anorg.  Chem.,  2,  235.     1892. 


304 


THE   ATOMIC    WEIGHTS. 


2. 


•3- 


5- 


Ni. 
.5870 
6011 

.7988 

•9913 

.9868 

.4093 
.7216 

•  3»94 


6. 


.4415 
.4350 
•  7752 

7-  1  .7667 
.7558 
•4555 
•4456 
.44415 
4423 
2508 
2467 


•4538 
.4451 
.4438 
.4272 
.2491 
.2467 
.3904 
.3891 


Oxidation  qf  Ni. 

NiO. 

•7471 

•7659 

.7606 
1.0175 
1.2631 
1.2582 

.5193 
.9200 
.4052 
.6518 
•5623 
•5556 
.9831 


1 


10. 


(  .3918 
1.3891 


.9639 

•5756 

.56765 

.5663 

.5642 

.3174 

.3H8 

.4976 

.4961 


78.839 
78.411 
78.368 
78.400 
78.481 
78.367 
78.457 
78.432 

Mean,  78.444,  =h  .0166 


Per  cent.  Ni. 

78.571 
78.372 
78.359 
78.506 
78.482 
78.429 
78.818 

78.435 
78.825 
78.414 

78.517 
78.294 

78.853 

78.515 
78.411 

79-135 
78.499 
78.43° 
78.394 
79-015 
78.367 

78.738 
78.432 


Mean,  78.557,  ±  .0319 


To  these  data  of  Kriiss  and  Schmidt  the  remarks  already  made  con- 
cerning Remmler's  work  seem  also  to  apply.  The  variations  appear  to 
be  fortuitous,  and  not  systematic,  although  the  authors  seem  to  think 
that  they  indicate  a  compositeness  in  that  substance  which  has  been 
hitherto  regarded  as  elementary  nickel.  There  is  doubtless  something 
to  be  said  on  both  sides  of  the  question ;  but  if  Kriiss  and  Schmidt  are 
right,  all  previous  atomic  weight  determinations  for  cobalt  and  nickel 
are  invalidated.  In  view  of  all  the  evidence,  therefore,  I  prefer  to  regard 
their  varying  estimations  as  affected  by  accidental  errors,  and  to  treat 
their  means  like  others.  On  this  basis,  their  work  combines  with  previ- 


NICKEL    AND    COBALT.  305 

ous  work  as  follows,  Schulzenberger's  measurements  of  the  ratio  NiO  :  Ni 
being  assigned  equal  weight  with  those  of  Mond,  Langer,  and  Quincke : 

Russell 78.593,  ±  .0018 

Zimmermann 78.582,  ±  .0006 

Mond,  Langer,  and  Quincke 78.545,  ±  .0061 

Schutzenberger 78.534,  ±  .0061 

Kriiss  and  Schmidt,  reduction  series 78.444,  ±  .0166 

Kriiss  and  Schmidt,  oxidation  series 78.557,  zh  .0319 

General  mean 78-57°,  db  .0006 

In  1889  Winkler  *  published  a  short  paper  concerning  the  gold  method 
for  determining  the  atomic  weights  in  question,  but  gave  in  it  no  actual 
measurements.  In  1893  f  he  returned  to  the  problem  with  a  new  line 
of  attack,  and  at  the  same  time  he  takes  occasion  to  criticise  Kriiss  and 
Schmidt  somewhat  severely.  He  utterly  rejects  the  notion  that  either 
nickel  or  cobalt  contain  any  hitherto  unknown  element,  and  ascribes  the 
peculiar  results  obtained  by  Kriiss  and  Schmidt  to  impurities  derived 
from  the  glass  apparatus  used  in  their  experiments.  For  his  own  part 
he  now  works  with  pure  nickel  and  cobalt  precipitated  electrolytically 
upon  platinum,  and  avoids  the  use  of  glass  or  porcelain  vessels  so  far 
as  possible.  With  material  thus  obtained  he  operates  by  two  distinct 
but  closely  related  methods,  both  starting  with  the  metal,  nickel  or 
cobalt,  converting  it  next  into  neutral  chloride,  and  then  measuring  the 
chloride  gravimetrically  in  one  process,  volumetrically  in  the  other. 

After  precipitation  in  a  platinum  dish,  the  nickel  or  cobalt  is  washed 
with  water,  rinsed  with  alcohol  and  ether,  and  then  weighed.  It  is  next 
dissolved  in  pure  hydrochloric  acid,  properly  diluted,  and  by  evapora- 
tion to  dryness  and  long  heating  to  150°  converted  into  anhydrous  chlo- 
ride. The  nickel  chloride  thus  obtained  dissolves  perfectly  in  water, 
but  the  cobalt  salt  always  gave  a  slight  residue  in  which  the  metal  was 
electrolytically  determined  and  allowed  for.  In  the  redissolved  chloride, 
by  precipitation  with  silver  nitrate,  silver  chloride  is  obtained,  giving  a 
direct  ratio  between  that  compound  and  the  nickel  or  cobalt  originally 
taken.  The  gravimetric  data  are  as  follows,  with  the  metal  equivalent 
to  100  parts  of  silver  chloride  given  in  a  final  column  : 

Nickel 


Ni. 

Aga. 

Ratio. 

.3011 

1.4621 

20.594 

.2242 

1.0081 

20.605 

.5166 

2.5108 

20.570 

.4879 

2.3679 

20.605 

•  3827 

1.8577 

20.601 

•  3603 

««75i7 

20.568 

Mean,  20.590, 

±  .0049 

*  Ber.  Deutsch.  Chem.  Gesell.,  22,  891. 
fZeit.  Anorg.  Chem.,  4,  10.     1893. 
20 


306 


THE    ATOMIC    WEIGHTS. 


Co. 

.3458 
•3776 

•4493 
.4488 
.2856 
.2648 


Cobalt. 

AgCl.  Ratio. 

1.6596  20.836 

1.8105  20.856 

2.1521  20.877 

2.1520  20.855 

1.3683  20.873 

1.2768  20.886 

Mean,  20.864,  ±  .0050 


In  the  volumetric  determinations  the  neutral  chloride,  prepared  as 
before,  was  decomposed  by  means  of  a  slight  excess  of  potassium  car- 
bonate, and  in  the  potassium  chloride  solution,  after  removal  of  the 
nickel  or  cobalt,  the  chlorine  was  measured  by  titration  by  Volhard's 
method  with  a  standard  solution  of  silver.  The  amount  of  silver  thus 
used  was  comparable  with  the  metal  taken. 

Nickel. 


Ni. 
.1812 
.1662 
.2129 
.2232 
.5082 
•1453 


Co. 

.177804 
.263538 
.245124 
.190476 
.266706 
•263538 


Af. 

.6621260 
.6079206 
•7775252 
.8162108 

.8556645 
.  53 r  504<> 


Cobalt. 


.6418284 
.9514642 
.8855780 
.6866321 
.9629146 
.9503558 


Ratio. 
27.366 

27.339 
27.382 
27.346 
27.386 
27.338 

Mean,  27.359,  ±  -OO59 


Ratio. 
27.702 
27.699 
27.679 

27.741 
27.696 

27-731 


Mean,  27.708,  ±  .0064 


In  view  of  the  possibility  that  the  cobalt  chloride  of  the  foregoing  ex- 
periments might  contain  traces  of  basic  salt;  Winkler,  in  a  supplement- 
ary investigation,*  checked  them  by  another  process.  To  the  electrolytic 
cobalt,  in  a  platinum  dish,  he  added  a  quantity  of  neutral  silver  sulphate 
and  then  water.  The  cobalt  gradually  went  into  solution,  and  metallic 
silver  was  precipitated.  The  weights  were  as  follows : 


Co. 

•  2549 
.4069 


Ag. 

.9187 
1.4691 


*  Zeit.  Anorg.  Chem.,  4,  462.     1893. 


NICKEL   AND    COBALT.  307 

On  examination  of  the  silver  it  was  found  that  traces  of  cobalt  were 
retained — less  than  0.5  mg.  in  the  first  determination  and  less  than  0.2 
mg.  in  the  second.  Taking  these  amounts  as  corrections,  the  two  experi- 
ments give  for  the  ratios  Ag.2 :  Co  :  :  100 :  x  the  subjoined  values  : 

27.706 
27.687 

These  figures  confirm  those  previously  found,  and  as  they  fall  within 
the  limits  of  the  preceding  series,  they  may  fairly  be  included  in  it,  when 
all  eight  values  give  a  mean  of  27.705,  ±  .0050. 

Still  another  method,  radically  different  from  all  of  the  foregoing  pro- 
cesses, was  adopted  by  Winkler  in  1894.*  The  metals  were  thrown  down 
electrolytically  upon  platinum,  and  so  weighed.  Then  they  were  treated 
with  a  known  excess  of  a  decinormal  solution  of  iodine  in  potassium 
iodide,  which  redissolved  them  as  iodides.  The  excess  of  free  iodine  was 
then  determined  by  titration  with  sodium  thiosulphate,  and  in  that  way 
the  direct  ratio  between  metal  and  haloid  was  ascertained.  The  results 
were  as  follows,  with  the  metal  proportional  to  100  parts  of  iodine  given 
in  the  third  column : 

Cobalt. 

WL  Co.  Wt.  I. 

2.128837 
2.166750 

First  series \  .5290  2.254335 

2.908399 
2.861617 

2.209694 

Second  series..  ^  .5267  2.246037 

2.268736 

Mean,  23.462,  ±  .0027 
Nickel. 

Wt.  Ni.  Wt.  I.  Ratio. 

.5144  2.217494  23.251 

.4983  2.148502  23.246 

First  series.. ..  ^  .5265  2.268742  23.260 

.6889  2.970709  23.243 

.6876  2.965918  23.237 

f.5120  2.205627  23.267 

Second  series.  .  1  .5200  2.240107  23.267 

(.5246  2.259925  23.267 


Mean,  23.255,  ±  .0091 

In  these  experiments,  as  well  as  in  some  previous'  series,  a  possible 
source  of  error  is  to  be  considered  in  the  occlusion  of  hydrogen  by  the 


*  Zeitsch.  Anorg.  Chem.,  8,  i.     1894. 


308  THE   ATOMIC   WEIGHTS. 

metals.  Accordingly,  in  a  supplementary  paper,  Winkler*  gives  the 
results  of  some  check  experiments  made  with  iron,  which,  however,  was 
not  absolutely  pure.  The  conclusion  is  that  the  error,  if  existent,  must 
be  very  small. 

In  1895  Hempel  and  Thiele's  work  on  cobalt  appeared.  f  First,  cobalt 
oxide,  prepared  from  carefully  purified  materials,  was  reduced  in  hydro- 
gen. The  weights  of  metal  and  oxygen  are  subjoined,  with  the  percent- 
age of  cobalt  in  the  oxide  deduced  from  them  : 

Co.  O.  Percentage. 

.90068  .24429  78.664 

.79159  .21445  78.686 

1.31558  .357i6  78.648 


Mean,  78.666,  ±  .0074 

This  mean  combines  with  former  means  as  follows  : 

Russell  ...........  .  .....................  78.592,  d=  .0023 

Zimmermann  ............................  78-635,  ±  .0002 

Retnmler  ............................  .*.  ,  78.613,  ±  .0099 

Hempel  and  Thiele  ......................  78.666,  ±  .0074 


General  mean 78.633,  ±  .0002 

In  their  next  series  of  experiments,  excluding  a  rejected  series,  Hempel 
and  Thiele  weighed  cobalt,  converted  it  into  anhydrous  chloride,  and 
noted  the  gain  in  weight.  In  four  of  the  experiments  the  chloride  was 
afterwards  dissolved,  precipitated  with  silver  nitrate,  and  then  the  silver 
chloride  was  weighed.  The  data  are  as  follows  : 

Co.  Cl  Taken  Up.  AgCl. 

.7010  -8453  

•3138  -3793  

.2949  .3562  1.4340 

.4691  .5657  2.2812 

.5818  .7026  2.8303 

.5763  .6947  

.5096  .6142  2.4813 

From  these  weights  we  get  two  ratios,  thus  : 


C72  :  Co  :  100  :  X, 

2AgCl  :  Co  :  :  IOO  :  x. 

82.929 

20.565 

82.731 

20.564 

82.791 

20.556 

82.924 

20.538 

82.807 

82.957 

Mean,  20.556,  ±  .0043 

82.970 

Mean,  82.873,  ±  .0241 

*  Zeitsch.  Anorg.  Chem.,  8,  291.     1895. 
fZeitsch.  Aiiorg.  Chem.,  n,  73. 


NICKEL   AND    COBALT.  309 

The  second  of  these  ratios  was  also  studied  by  Winkleiyand  the  two 
series  combine  as  follows  : 

Winkler 20.864,  =b  .0050 

Hempel  and  Thiele.^. 20.556,  rb  .0043 

General  mean 20.687,  =b  -OO33 

Hempel  and  Thiele  apply  to  it  a  correction  for  silver  chloride  retained 
in  solution,  but  its  amount  is  small  and  not  altogether  certain.  For 
present  purposes  the  correction  may  be  neglected. 

For  the  atomic  weight  of  nickel  we  now  have  ratios  as  follows  : 

(I.)  Per  cent,  of  Ni  in  NiC,O4.3H2O,  29.084,  ±  .006 

(2.)  Per  cent,  of  CO2  from  NiC2O4.2H2O,  44.098,  rb  .027 

(3.)  Per  cent,  of  Ni  in  NiC2O4.2H2O,  31.408,  ±  .0026 

(4.)  Per  cent,  of  CO2  from  NiC2O4.2H2O,  47.605,  =h  .053 

(5.)  Per  cent,  of  Ni  in  brucia  nickelocyanide,  5.7295,  ±  .0034 

(6.)  Per  cent,  of  Ni  in  strychnia  nickelocyanide,  6.595,  =fc  .005 

(7.)  Per  cent,  of  NiO  in  NiSO4,  48.269,  rb  .018 

(8.)  Per  cent,  of  Ni  in  NiO,  78.570,  ±  .0006 

(9.)  Ag2  :  NiCl2  :  :  100  :  60.194,  rb  .0061 

(10.)  2AgCl  :  Ni  :  :  100  :  20.590,  rb  .0049 

(n.)  Ag2  :  Ni  :  :  100  :  27.359,  ±  •°°$9 

(12.)  Au2  :  Ni3  :  :  100  :  45.209,  ±  .019 

(13.)  BaSO4  :  K2Ni(SO4)2.6H2O  :  :  100  :  93.6505.  ±  .001 

(14.)  Ni  :  H2  :  :  100  :  3.4211,  ±  .001 

(15.)  I2  :  Ni  :  :  IOO  :  23.255,  ±  .0091 

To  the  reduction  of  these  ratios  the  following  atomic  and  molecular 
weights  are  applicable : 

O     =     15.879,  db  .0003  I          =  125.888,  rb  .0069 

C     =»     11.920,  rb  .0004  K         —    38.817,1^.0051 

N    =    13.935,  rb  .0021  Ba      =  136.392,  ±  .oo86 

S      =    31.828,  rb. 0035  Au       =  195.743,  rb  .0049 

Ag  =  107.108,  rb  .0031  AgCl=  142.287,  rb  .0037 
Cl    =    35-T79,  ±.0048 

Since  the  proportion  of  water  in  the  oxalates  is  not  an  absolutely  cer- 
tain quantity,  the  data  concerning  them  can  be  best  handled  by  employ- 
ing the  ratios  between  carbon  dioxide  and  the  metal.  Accordingly,  ratios 
(1)  and  (2)  give  a  single  value  for  Ni,  and  ratios  (3)  and  (4)  another.  In 
all,  there  are  thirteen  values  for  the  atomic  weight  in  question  : 

From  (i)  and  (2) Ni  =  57.614,  rb  .0372 

From  (5) "  =57.625,  rb. 0343 

From  (3)  and  (4) "  =  57.635,  rb  .0644 

From  (6) "  =  57.687,  rb  .0439 

From  (8) "  =  58.218,  rb  .0020 

From  (7) "  —  58.268,  ±  .0428 

From  (13) "  =  58.448,  rb  .0206 


310  THE    ATOMIC    WEIGHTS. 

From  (14) Ni  —  58.456,  ±  .0316 

From  (15) , "  =  58.551,  rb  .0231 

From  (9)    "  =  58.587,  =b  .0179 

From  (10) . .    . "  =  58.594,  ±  .0141 

From  (u)...  . "=58.607,^.0128 

From  (12.) "  =  58.994,  zb  .0248 

General  mean Ni  =  58.243,  ±  .0019 

If  0  =  16,  this  becomes  Ni  =  58.687. 

It  is  quite  evident  here  that  ratio  (8),  which  includes  the  marvelously 
concordant  determinations  of  Zimmermann,  far  outweighs  all  the  other 
data.  Whether  so  excessive  a  weight  can  justifiably  be  assigned  to  one 
set  of  measurements  is  questionable,  but  the  general  mean  thus  reached 
is  not  far  from  midway  between  the  highest  and  lowest  of  the  values,  and 
hence  it  may  fairly  be  entitled  to  provisional  acceptance.  No  one  of  the 
individual  values  rests  upon  absolutely  conclusive  evidence,  so  that  no 
one  can  be  arbitrarily  chosen  to  the  exclusion  of  the  others.  Further 
investigation  is  evidently  necessary. 

For  cobalt  we  have  sixteen  ratios,  as  follows  : 

(i.)   Per  cent,  of  Co  in  CoC2O4.2H2O,  32.5555,  ±  .0149 

(2.)   Per  cent,  of  CO2  from  CoC204.2H2O,  47-7475,  =b  .0213 

(3.)   Per  cent,  of  Co  in  CoO,  78.633,  ±  .0002 

(4.)  Per  cent,  of  Co  in  purpureocobalt  chloride,  23.6045,  ±  .0018 

(5.)  Per  cent,  of  Co  in  phenylammonium  cobalticyanide,  11.8665,  ±  .0124 

(6.)   Per  cent,  of  Co  in  ammonium  cobalticyanide,  21.943,  ±  .029 

(7.)   Per  cent,  of  Co  in  brucia  cobalticyanide,  3.7437,  zb  .0036 

(8.)  Per  cent,  of  Co  in  strychnia  cobalticyanide,  4.5705,  zb  .005 

(9.)   Per  cent,  of  CoO  in  CoSO4,  48.287,  ±  .0135 

(10.)  Ag2  :  CoCl2  :  :  100  :  60.200,  ±  .0095 

(n.)  2AgCl  :  Co  :  :  100  :  20.687,  zb  .0033 

(12.)  Ag2  :  Co  :  :  100  :  27.705,  ±  .0050 

(13.)  Au2  :  Co3  :  :  100  :  45.151,  ±  .025 

(14.)  Co  :  H2  :  :  100  :  3.4110,  ±  .0009 

(15.)  T2  :  Co  :  :  100  :  23.462,  ±  .0027 

(16.)  C12  :  Co  :  :  100  :  82.873,  ±  .0241 

From  these,  using  the  atomic  weights  already  cited  under  nickel,  and 
combining  ratios  (1)  and  (2),  we  get — 

From  (16) Co  =  58.308,  zb  .0187 

From  (9) "  =.  58.321,  ±  .0288 

From  (3) "  =  58.437,  ±  .0014 

From  (i o) "=  58.600,  ±  .0228 

From  (14) "  =  58.630,  ±  .0286 

From  (5) "  =  58.639,  db  .0619 

From  (8) "  =  58.696,  =b  .0642 

From  (6) "  —  58.736,  ±  .0808 

From  (4) "  =58.774,  ±  .0071 

From  (7) "  =  58.791,  ±  .0566 


RUTHENIUM.  311 

From  (i  i) Co  =  58.870,  ±  .0094 

From  (13) "  —58.920,  ±  .0327 

From  (15) "  =  59.072,  ±  .0075 

From  (12) "  =  59.349,  ±  .0108 

From  (i)  and  (2) "  =  59-562,  ±  .0382 

General  mean , Co  =  58.487,  ±  .0013 

If  0  =  16,  this  becomes  Co  =  58.932. 

Here  again  the  oxide  ratio,  because  of  Zimmermann's  work,  receives 
excessive  and  undue  weight.  The  arithmetical  mean  of  the  fifteen  values 
is  Co  =  58.781.  Between  this  and  the  weighted  general  mean  the  truth 
probably  lies,  but  the  evidence  is  incomplete,  and  more  determinations 
are  needed. 


RUTHENIUM. 

The  atomic  weight  of  this  metal  has  been  determined  by  Claus  and 
by  Joly.  Although  Claus*  employed  several  methods,  we  need  only 
consider  his  analyses  of  potassium  rutheniochloride,  K2RuCl5.  The  salt 
was  dried  by  heating  to  200°  in  chlorine  gas,  but  even  then  retained  a 
trace  of  water.  The  percentage  results  of  the  analyses  are  as  follows^ 

Ru.  2KCI.  C/3. 

28.96  40.80  30.24 

28.48  41.39  30.22 

28.91  41.08  30.04 

Mean,  28.78  41.09  30.17 

Reckoning  directly  from  the  percentages,  we  get  the  following  dis- 
cordant values  for  Ru  : 

From  percentage  of  metal Ru  =  102.45 l 

From  percentage  of  KC1 "  =  106.778 

From  percentage  of  C13 "  =    96.269 

These  results  are  obviously  of  little  importance,  especially  since  the 
best  of  them  is  not  in  accord  with  the  position  of  ruthenium  in  the 
periodic  system.  The  work  of  Joly  is  more  satisfactory. f  Several  com- 
pounds of  ruthenium  were  analyzed  by  reduction  in  a  stream  of  hy- 
drogen with  the  following  results  : 

*  Journ.  fur  Prakt.  Chem.,  34,  435.     1845. 
fCompt.  Rend.,  108,  946. 


312  THE   ATOMIC    WEIGHTS. 

First,  reduction  of  Ru02  : 


Ru.  Per  cent.  Ru. 
2.1387            1.6267  76.060 

2.5846  1.9658  76.058 

2.3682  i.  8016  76.075 

2.8849  2-J939  76.046 


Mean,  76.060,  rb  .0040 


Second,  reduction  of  the  salt  RuCl3.NO.H20 : 

Per  cent.  Ru. 

39-78 
39.66 

Mean,  39.72,  ±.  0405 

Third,  reduction  of  RuCl3.N0.2NH4Cl : 

Per  cent.  Ru. 
29.44 
29.47 


Mean,  29.455,  ±  .0101 

Computing  with  0  =  15.879,  ±  .0003 ;  N  =  13.935,  ±  .0021,  and  Cl  = 
35.179,  =h  .0048,  these  data  give  three  values  for  ruthenium,  as  follows: 

1.  From  RuO2 Ru  =  100.922,  ±  .0178 

2.  From  RuCl3.NO.H2O "  =  100.967,  ±  .  1 102 

3.  From  RuCl3.NO.2AmCl "   =  100.868,  ±  .0387 

General  mean Ru  =  100.913,  ±  .0160 

If  0  =  16,  Ru=101.682. 


RHODIUM.  313 


RHODIUM. 

Berzelius  *  determined  the  atomic  weight  of  this  metal  by  the  analysis 
of  sodium  and  potassium  rhodiochlorides,  Na3RhCl6,  and  K2RhCl5.  The 
latter  salt  was  dried  by  heating  in  chlorine.  The  compounds  were  ana- 
lyzed by  reduction  in.  hydrogen,  after  the  usual  manner.  Reduced  to 
percentages,  the  analyses  are  as  follows  : 

In  Na,RhCl6. 

Rh.  3NaCl.  <T/3. 

26.959  45.853  27.189 

27.229  45-301  27.470 

......  ......  27.616 

Mean,  27.094  Mean,  45.577  Mean,  27.425 

In  K 


Rh.  2KCI.  CI3. 

28.989  41-450  29.561 

From  the  analyses  of  the  sodium  salt  we  get  the  following  values  for 
Rh: 

P'rom  per  cent,  of  metal  ....................  Rh  =  104.191 

From  per  cent,  of  NaCl  ....................  "  =  102.449 

From  per  cent,  of  C13  .....................  "   =  105.103 

From  ratio  between  C13  and  Rh  .........  .....  "  =  104.263 

From  ratio  between  NaCl  and  Rh  ......  .....  "   =  103.544 

These  are  discordant  figures  ;  but  the  last  one  fits  in  fairly  well  with 
the  values  calculated  from  the  potassium  compound,  which  are  as 
follows  : 

From  per  cent,  of  metal  ....................  Rh  —  103.499 

"    From  per  cent,  of  KC1  .....................  "    =  103.648 

From  per  cent,  of  C13  ......................  "   =  103.485 

From  Rh  :  C13  ratio  ........................  '-   =  103.495 

From  Rh  :  KC1  ratio  .......  .  .............  "   =  103.540 


Mean Rh  =  103.533 

If  0  =  16,  this  becomes  Rh  =  104.323. 

Jorgensen's  determination,!  so  far  as  I  can  ascertain,  was  published 
only  as  a  preliminary  note,  to  the  effect  that  the  atomic  weight  of  rho- 
dium is  103,  nearly.  No  details  are  given. 

*  Poggend.  Annalen,  13,  435.     1828. 
t  Journ.  fur  Prakt.  Chem.  (2),  27,  486. 


314  THE    ATOMIC    WEIGHTS. 

Seubert  and  Kobbe  *  determine  the  atomic  weight  by  igniting  rhodium 
pentamine  chloride  in  hydrogen,  and  weighing  the  residual  metal.  Their 
results  are  given  below  : 


3.  Rh.                           Per  cent.  Rh. 

1.8585  .6496  34-953 

I-556o  .5435  34.929 

1.5202  .5310  34-93° 

2.  01  1  1  .7031  34.961 

1.8674  .6528  34.958 

2-4347  .8513  34-965 

2.3849  .8338  34.962 

2.5393  .8881  34-974 

1.4080  .4920  34-943 

1.4654  .5123  34.960 


Mean,  34-954,  ±  -0032 

In  the  sixth  experiment  the  ammonium  chloride  formed  was  collected 
in  a  bulb  tube,  and  estimated  by  weighing  as  silver  chloride.  3.5531 
grms.  of  AgCl  were  obtained. 

Computing  with  N  =13.935,  ±  .0021  ;  Cl  =35.179,  ±  -0048,  and  AgCl  = 
142.287,  ±  .0037,  we  have— 

From  per  cent,  of  metal  ............  Rh  =  102.215,  ±  .0143 

From  AgCl  ratio  ................       "   =  102.287,  =b  .0324 


General  mean Rh  =  102.227,  ±  .0131 

If  0  =  16,  Rh  =  103.006. 

In  the  second  of  these  values  the  probable  error  given  is  only  that  due 
to  the  antecedent  atomic  weights  of  N,  Cl,  and  AgCl.  It  is  therefore 
lower  than  it  should  be.  The  two  values,  however,  are  fairly  in  agree- 
ment, and  the  result  is  satisfactory. 

*  Ann.  d.  Chem.,  260,  318.     1890. 


PALLADIUM.  315 


PALLADIUM. 

The  first  work  upon  the  atomic  weight  of  palladium  seems  to  have 
been  done  by  Berzelius.  In  an  early  paper*  he  states  that  100  parts  of 
the  metal  united  with  28.15  of  sulphur.  Hence  Pd  =  113.06,  a  result 
which  is  clearly  of  no  present  value. 

In  a  later  paper  f  Berzelius  published  two  analyses  of  potassium  pal- 
ladiochloride,  K2PdCl4.  The  salt  was  decomposed  by  ignition  in  hydro- 
gen, as  was  the  case  with  the  double  chlorides  of  potassium  with  platinum, 
osmium,  and  iridium.  Reducing  his  results  to  percentages,  we  get  the 
following  composition  for  the  substance  in  question  : 

Pd.  2KCL  C/2. 

32.726  46.044  21.229 

32.655  45-741  21.604 

Mean,  32.690  Mean,  45.892  Mean,  21.416 

From  these  percentages,  calculating  directly,  very  discordant  results 
are  obtained : 

From  percentage  of  metal   Pd  =  106.53 

From  percentage  of  KC1 "  =  104.13 

From  percentage  of  C12  (loss) "  =  1 10.20 

Obviously,  the  only  way  to  get  satisfactory  figures  is  to  calculate  from 
the  ratio  between  the  Pd  and  2KC1,  eliminating  thus  the  influence  of 
water  in  the  salt.  The  two  experiments  give,  as  proportional  to  100 
parts  of  KC1,  the  following  of  Pd : 

71-075 
7i. 391 

Mean,  71.233,  ±.1066 

Hence  Pd  =  105.419. 

In  1847  Quintus  Icilius  J  published  a  determination,  which  need  be 
given  only  for  the  sake  of  completeness.  He  ignited  potassium  palladio- 
chloride  in  hydrogen,  and  found  the  following  amounts  of  residue.  His 
weights  are  here  recalculated  into  percentages  : 

64.708 
64.965 
64.781 


Mean,  64.818 

From  this  mean,  Pd=  111.258.     This  result  has  no  present  value. 

*Poggend.  Annalen,  8,  177.     1826. 
t  Poggend.  Annalen,  13,  454.     1828. 

I  "Die  Atomgewichte  vom  Pd,  K,  Cl,  Ag,  C,  und  H,  nach  der  Methode  der  kleinsten  Quadrate 
berechnet."     Inaug.  Diss.    Gottingen,  1847.     Contains  no  other  original  analyses. 


316 


THE    ATOMIC    WEIGHTS. 


In  1889  Keiser's  first  determinations  of  this  constant  appeared.*  Find- 
ing the  potassium  palladiochloride  to  contain  u  water  of  decrepitation," 
he  abandoned  its  use,  and  resorted  to  palladiammonium  chloride, 
Pd(NH3Cl)2,  as  the  most  available  compound  for  his  purpose.  This 
salt,  heated  in  hydrogen,  yields  spongy  palladium,  which  was  allowed 
to  cool  in  a  current  of  dry  air,  in  order  to  avoid  gaseous  occlusions.  The 
salt  itself  was  dried,  previous  to  analysis,  first  over  sulphuric  acid,  and 
then  in  an  air  bath  at  a  temperature  from  120°  to  130°.  Two  series  of 
experiments  were  made,  the  second  series  starting  out  from  palladium 
produced  by  the  first  series.  The  data  are  as  follows : 


Pd(NH,Cl},. 
.83260 
.72635 
.40280 
•57940 
.89895 
.48065 

•56015 

.82658 
2.40125 
1.10400 

•93310 


First  Series. 
Pd. 

•41965 
.86992 
.70670 
.79562 
.95650 
•74570 
.78585 
.92003 
1.20970 
.55629 
.47010 


Percent.  Pd. 
50.402 

50-391 
50.378 
50.375 
50.370 
50-363 
50.370 
50-369 
50.378 
50.389 
50.380 


Reduced  to  vacuum  this  becomes  50.360, 

Second  Series. 


Pd. 

1.31900 
1.12561 

.87445 
.85210 
.86825 

.56535 

.59200 

1.22280 


2.61841 
2.23420 

•73553 
.69160 
.72403 

.12222 

•17457 
2.42760 


Mean,  50.379,  ±  .0008 


Per  cent.  Pd. 

50.374 
50-381 
50.385 
50.372 
50.362 
50.378 
50.401 
50-37I 


Mean,  50.378, 
Reduced  to  vacuum,  50.359 


.0028 


The  reductions  to  vacuum  are  neglected  by  Keiser  himself,  but  are  here 
added  in  order  to  secure  uniformity  with  later  results  by  the  same  author. 
The  mean  of  both  series,  thus  corrected,  gives  Pd  —  105.74. 

Bailey  and  Lamb  f  made  experiments  upon  several  compounds  of  pal- 
ladium, but  finally  settled  upon  palladiammonium  chloride,  like  Keiser. 


*Am.  Chem.  Journ.,  n,  398.     1889. 
t  Journ.  Chem.  Soc.,  61,  745.     1892. 


PALLADIUM.  317 

Two  preliminary  experiments,  however,  with  potassium  palladiochloride 
are  given,  in  which  the  salt  was  reduced  in  hydrogen,  and  both  Pd  and 
KC1  were  weighed.  The  data  are  as  follows,  with  the  ratio  (calculated 
as  with  Berzelius'  experiments)  given  in  a  third  column : 

2KCI.  Pd.  Ratio. 

1.49767  1.05627  70.528 

.90484  .63738  70.441 

Mean,  70.485,  ±  ,0290 

Hence  Pd  =  104.312. 

The  palladiammonium  chloride  was  studied  by  two  methods.  First, 
weighed  quantities  of  the  salt  were  reduced  in  hydrogen,  the  ammonium 
chloride  so  formed  was  collected  in  an  absorption  apparatus,  and  then 
precipitated  with  silver  nitrate.  The  weights  found  were  as  follows,  with 
the  Pd(NH3Cl)2  proportional  to  100  parts  of  silver  chloride  given  in  the 
third  column  : 


AgCl.  Ratio. 

24276                           1.682249  73.879 

08722                           1.468448  %                74.040 

47666                          2.000164  73.828 

34887                           1.837957  73.390 

74569                          2.362320  73-898 


Mean,  73.807,  ±  .0742 


Hence  Pd  =  105.808.  Bailey  and  Lamb  regard  this  as  too  high,  and 
suspect  loss  of  NH4C1  during  the  operation. 

The  second  series  of  data  resemble  Reiser's.  The  salt  was  reduced  in 
hydrogen,  and  the  spongy  palladium  was  weighed  in  a  Sprengel  vacuum. 
The  data  are  as  follows  : 

Pd(NHzCr}v                            Pd.  Per  cent.  Pd. 

A    f  1.890597                              -947995  50-H3 

'  (  1.874175                              .940271  50.170 

( 1.307076                              .654687  50.088 

B    !  1.340045                              .633207  50.238 

'1  1-905536                             .955950  5°-l67 

1 1.685582                             .846472  50.218 

1.691028                             .849120  50.213 

2.112530                           1.059690  50.162 

2.110653                            1.057910  50.122 

1.969100                             .988155  50.184 


Mean,  50.171,  ±  .0099 

Hence  Pd  =  104.943.     Bailey  and  Lamb's  weighings  are  all  reduced 
to  a  vacuum. 


Ml: 


318  THE   ATOMIC   WEIGHTS. 

Keller  and  Smith,*  reviewing  Reiser's  work,  find  that  palladiam- 
monium  chloride,  prepared  as  Keiser  prepared  it,  may  retain  traces  of 
foreign  metals,  and  especially  of  copper.  Accordingly,  they  prepared  a 
quantity  of  the  salt,  after  a  thorough  and  elaborate  process  of  purifica- 
tion, dried  it  with  extreme  care,  and  then  determined  the  palladium  by 
electrolysis  in  silver-coated  .platinum  dishes.  The  precipitated  palladium 
was  dried  under  varying  conditions,  concerning  which  the  original  me- 
moir must  be  consulted,  and  was  proved  to  be  free  from  occluded  hydro- 
gen. By  this  method  two  sets  of  experiments  were  made  to  determine 
the  atomic  weight  of  palladium ;  but  for  present  purposes  the  two  may 
fairly  be  treated  as  one.  The  data  obtained  are  as  follows,  but  the 
weights  do  not  appear  to  have  been  reduced  to  a  vacuum : 

Pd(NH^Cl\.  Pd.  Percent.  Pd. 

C  i.  29960  .65630  50-504 

A.  J  1.05430  .53253  50.51° 

(i.92945  -97455  50509 

f  i. 94722  .98343  50.504 

1.08649  .54870  50.502 

28423  .64858  50.503 

68275  .  .85010  S°-519 

1.69113  -85431  5o.5J7 

1.80805  .91310  50.502 

Mean,  50.508,  =b  .0014 

Hence  Pd  —  106.368,  a  result  notably  higher  than  Reiser's. 

Reller  and  Smith  account  for  the  difference  between  their  determina- 
tions and  Reiser's  partly  by  the  assumption  that  the  materials  used  by 
the  latter  were  not  pure,  and  partly  by  considerations  based  on  the  pro- 
cess. In  order  to  clarify  the  latter  part  of  the  question  they  made  three 
sets  of  experiments  by  Reiser's  method,  slightly  varying  the  conditions. 
First,  the  chloride  was  not  pulverized  before  ignition,  and  slight  decrepi- 
tation took  place,  while  dark  stains  of  palladium  appeared  in  the  reduc- 
tion tube,  indicating  loss  by  volatilization.  Secondly,  the  chloride  was 
prepared  from  crude  palladium  exactly  as  described  by  Reiser,  but  was 
pulverized  before  reduction.  No  decrepitation  ensued,  but  traces  of  pal- 
ladium were  volatilized.  The  third  series,  also  on  finely  pulverized 
material,  was  like  the  second ;  but  the  palladiammonium  chloride  was 
purified  by  Reller  and  Smith's  process.  The  three  series,  here  treated 
as  one,  are  as  follows : 

Pd(NHzCl)v  Pd.  Per  cent.  Pd. 

.62955  -3r743                             50-422 

First  series....  J     -77*70  .38942                               5O-397 

.83252  .41918                             50.350 

•99°55  .49895  50.371 

*Amer.  Cheni.  Journ.,  14,  423.     1892. 


PALLADIUM.  319 

Pd(NH.ACl}r  Pd.  Percent.  Pd. 

.51468  5°-372 

•55590  50.388 

Second  series.  J     '6669O  -33590  50.367 

•43733  50-360 

•71255  50.382 

.58050  50.376 

.48502  50.403 

Third  series...^     •»"*<*  «49294  50.401 

•47517  50.4H 

•43405  50-430 

Mean,  50.388,  ±  .0043 

The  three  series  seem  to  be  fairly  in  agreement  between  themselves, 
and  with  Reiser's  work,  but  diverge  seriously  from  the  electrolytic  data. 

Keller  and  Smith  also  attempted  to  determine  the  atomic  weight  of 
palladium  by  heating  the  palladiammonium  chloride  in  sulphuretted 
hydrogen,  and  so  converting  it  into  the  sulphide,  PdS.  These  data  were 
obtained : 

Pd(NH.iCl)^  PdS.  Percent.  CdS. 

.71699  .47066  65.644 

1.31688  .86445  65.659 


Mean,  65.651,  ±  .0051 

Hence  Pd  =-.  106.55.  This  result,  however,  is  affected  by  the  work  of 
Petrenko-Kritschenko,*  who  has  shown  the  existence  of  the  sulphide 
PdS  to  be  uncertain. 

Joly  and  Leidie,f  in  their  determinations  of  this  atomic  weight,  re- 
turned to  the  potassium  palladiochloride,  K2PdCl4.  In  their  first  series 
of  experiments  the  salt  was  dried  in  vacuo  at  ordinary  temperatures.  It 
was  then  electrolyzed  in  a  solution  acidulated  with  hydrochloric  acid, 
both  the  deposited  palladium  and  the  potassium  chloride  being  weighed. 
The  palladium  was  dried,  ignited  in  a  stream  of  hydrogen,  and  cooled  in 
an  atmosphere  of  carbon  dioxide.  The  results  were  as  follows,  with  the 
column  added  by  me  giving  the  Pd  equivalent  to  100  parts  of  KC1 : 
K,PdCl,.  Pd.  2KCl.  Ratio. 

1.0255  .3919  -5520  70.996 

1.2178  .3937  .5551  70.924 

1.2518  .4048  .5687  71.016 

Mean,  70.979,  =b  .0188 

This  series  was  rejected  by  the  authors,  because  the  salt  was  found  to 
contain  water — in  one  case  0.23  per  cent.  This  error,  however,  should 

«  *Zeit.  Anorg.  Chem.,  4,  251.     1893. 

t  Compt.  Rend.,  116,  147.     1893. 


320  THE   ATOMIC   WEIGHTS. 

not  invalidate  the  Pd  :  KC1  ratio.     In  a  second  series  the  palladiochlo- 
ride  was  dried  in  vacuo  at  100°,  giving  the  following  data  : 


Pd.  zKCl.  Ratio. 

1.3635                        .4422  .6186  7M84 

3.0628                        .9944  i.3929  7I-39I 

1.4845                        .4816  .6782  71.011 

1.7995                        -5838  .8206  7M43 


Mean,  71.257,  db  .0736 

These  experiments  seem  to  be  less  concordant  than  the  preceding  set. 
It  must  be  noted,  however,  that  the  authors  reject  the  KC1  determina- 
tions and  compute  directly  from  the  ratio  between  the  salt  and  the  metal. 
But  the  ratio  here  chosen  agrees  best  with  the  determinations  made  by 
other  observers,  giving  for  this  series  the  mean  value  Pd  =  105.455,  and 
is,  moreover,  uniform  with  the  data  given  by  Berzelius  and  by  Bailey 
and  Lamb. 

Joly  and  Leidie  also  give  two  experiments  made  by  reducing  the 
K2PdCl4  in  hydrogen,  with  the  subjoined  results  : 


Pd.  2KCL  Ratio. 

2.4481  -7949  1.1168  7LI77 

1.8250  .5930  .8360  70  933 


Mean,  71.055,  rb  .0823 

Combining  these  data  with  previous  series,  we  have — 

Berzelius 7I-233,  ±  .1066 

Bailey  and  Lamb 70.485,  ±  .0290 

Joly  and  Leidie,  first 70.979,  ±  .0188 

Joly  and  Leidi£,  second 7I-257,  =b  -°736 

Joly  and  Leidie,  third 71.055,  ±  .0823 

General  mean 70.865,  d=  .0150 

In  view  of  the  discordance  among  the  determinations  hitherto  cited 
and  because  of  the  criticisms  made  by  Keller  and  Smith,  Keiser,  jointly 
with  Miss  Mary  B.  Breed,*  repeated  his  former  work,  with  some  varia- 
tions and  added  precautions  to  ensure  accuracy.  His  general  method 
was  the  same  as  before,  namely,  the  reduction  of  palladiammonium 
chloride  by  a  stream  of  hydrogen.  First,  palladium  was  purified  by 
distillation  as  PdCl2  at  low  red  heat  in  a  current  of  chlorine.  From  this 
chloride  the  palladiammonium  salt  was  then  prepared.  Upon  heating 
the  compound  gently  in  a  stream  of  hydrogen,  decomposition  ensued 
absolutely  without  decrepitation  or  loss  of  palladium  by  volatilization. 
Neither  source  of  error  existed.  The  results  obtained  were  these  : 

*Am.  Chetn.  Journ.,  16,  20.     1894. 


PALLADIUM.  321 

Pd(NH,Cl\.  Pd.  Per  cent.  Pd. 

1.60842  .80997  50-358 

2.08295  1.04920  50.371 

2.02440  1-01975  50.373 

2.54810  1.28360  50.375 

I-75505  .88410  50-375 


Mean,  50.370,  ±  .0023 
Reduced  to  vacuum,  50.351 

In  a  second  series  of  experiments,  palladium  was  purified  as  in  the 
earlier  investigation,  but  with  special  care  to  eliminate  rhodium,  iron, 
copper,  gold,  mercury,  etc.  The  palladiammoniura  salt  prepared  from 
this  material  gave  as  follows  : 

Pd(NH.ACl}r  Pd.  Per  cent.  Pd. 

1.50275  .75685                              50.364 

1.23672  .62286                              50-365 

1-34470  .67739                              50.375 

i  .49°S9  .75095                              50-379 


Mean,  50.371,  i  .0026 
Reduced  to  vacuum,  50.352 

Here,  again,  no  loss  from  decrepitation  or  volatilization  occurred, 
although  evidence  of  such  loss  was  carefully  sought  for.  The  data  thus 
obtained  may  now  be  combined  with  the  previous  series,  thus  : 

Keiser,  first  series 50.360,  dr  .0008 

Keiser,  second  series 5°-359,  =b  .0028 

Bailey  and  Lamb 50. 171,  ±  .0099 

Keller  and  Smith,  electrolytic 50.508,  rh  .0014 

Keller  and  Smith,  hydrogen  series 50.388,  dr  .0043 

Keiser  and  Breed,  first  series 5O-351,  =b  .0023 

Keiser  and  Breed,  second  series 5°-352>  ±  .0026 


General  mean 50.388,  dr  .00062 

For  palladium,  ignoring  the  work  of  Quintus  Icilius,  the  subjoined 
ratios  are  now  available : 

(i.)  2KC1  :  Pd  :  :  100  :  70.865,  dr  .0150 
(2.)   Per  cent.  Pd  in  Pd(NH3Cl),,  50.388,  dr  .00062 
(3.)   2AgCl  :  Pd(NH3Cl)2  :  :  100  :  73.807,  dr  .0742 
(4.)   Pd(NH3Cl)2  :  PdS  :  :  100  :  65.651,  dr  .0051 

The  antecedent  data  are — 

Cl  =  35.179,  i  .0048  S        =    3 1." 828,  +3  .0015 

•K  =  38.817,  ±  .0051  AgCl  =  142.287,  ±  .0037 

N  =  13.935,  dr  .C02I 

21 


THE    ATOMIC    WEIGHTS. 

Hence,  for  the  atomic  weight  of  palladium,  we  have — 

From  (i) Pd  =  104.874,  it  .0243 

From  (2) "   —  105.858,  ±  .0200 

From  (3) "  =  105.808,  ±  .2117 

From  (4) "  =  106.550,  =b  .0491 


General  mean I'd  —  105.556,  ±  .0147 

With  O  =  16,  Pd  =  106.364. 

Taking  the  values  separately,  the  second  is  probably  the  best ;  but  in 
view  of  the  work  done  by  Bailey  and  Lamb  on  one  side,  and  by  Keller 
and  Smith  on  the  other,  it  cannot  be  accepted  unreservedly.  Until  the 
cause  of  variation  in  the  results  is  clearly  determined,  it  is  better  to  take 
the  general  mean  of  all  the  data,  as  given  above. 


OSMIUM. 

The  atomic  weight  of  this  metal  has  been  determined  by  Berzelius,  by 
Fremy,  and  by  Seubert. 

Berzelius  *  analyzed  potassium  osmichloride,  igniting  it  in  hydrogen 
like  the  corresponding  platinum  salt.  1.3165  grammes  lost  .3805  of 
chlorine,  and  the  residue  consisted  of  .401  grm.  of  potassium  chloride, 
with  .535  grm.  of  osmium.  Calculating  only  from  the  ratio  between  the 
Os  and  the  KC1,  the  data  give  Os  =  197.523. 

Fremy's  determination  f  is  based  upon  the  composition  of  osmium 
tetroxide.  No  details  as  to  weighings  or  methods  are  given ;  barely  the 
final  result  is  stated.  This,  if  0  =  16,  is  Os  =  199.648. 

When  the  periodic  law  came  into  general  acceptance,  it  became  clearly 
evident  that  both  of  the  foregoing  values  for  osmium  must  be  several 
units  too  high.  A  redetermination  was  therefore  undertaken  by  Seubert,J 
who  adopted  methods  based  upon  that  of  Berzelius.  First,  ammonium 
osmichloride  was  reduced  by  heating  in  a  stream  of  hydrogen.  The 
residual  osmium  was  weighed,  and  the  ammonium  chloride  and  hydro- 
chloric acid  given  off  were  collected  in  a  suitable  apparatus,  so  that  the 
total  chlorine  could  be  estimated  as  silver  chloride.  The  weights  were 
as  follows : 

Am2OsClB.                             Os.  6AgCl. 

1.8403  7996  3.5897 

2.0764  .9029  4.0460 

2.1501  .9344  .  4.195° 

2.1345  .9275  4.1614 

*Poggend.  Annalen,  13,  530.     1828. 

fCompt.  Rend.,  19,  468.     Journ.  fiir  Prakt.  Chem.,  31,  410.     1844. 

J  Bericnte  Deutsch.  Chem.  Gesell.,  21,  1839.     l888- 


OSMIUM.  323 

Hence  we  have  for  the  percentage  of  osmium  and  for  the  osmichloride 
proportional  to  100  parts  of  AgCl — 

Per  cent.  Os.  AgCl :  Salt. 

43.446  51.266 

43.484  $1.32° 

43-458  51-254 

43-453  5L293 


Mean,  51.283,  ±  .0099 


In  a  later  paper  *  two  more  reductions  are  given,  in  which  only  osmium 
was  estimated. 

Sail.  Os.  Percent.  Os. 

2.6687  1.1597  43.456 

2.6937  1.1706  43-457 

These  determinations,  included  with  the  previous  four  as  one  series, 
give  a  mean  percentage  of  Os  in  Am2OsCl6  of  43.459,  ±  .0036. 

Secondly,  potassium  osmichloride  was  treated  in  the  same  way,  but 
the  residue  weighed  consisted  of  Os  +  2KC1.  From  this  the  potassium 
chloride  was  dissolved  out,  recovered  by  evaporating  the  solution,  and 
weighed  separately.  The  volatile  portion,  4HC1,  was  also  measured  by 
precipitation  as  silver  chloride.  In  Seubert's  first  paper  these  data  are 
given  : 

Os.  2KCI.  4AgCl. 


2.5148  .....                      .7796                     2.9837 

2.1138  .8405                      .6547                     2.5076 

Hence,  with  salt  proportional  to  100  parts  of  AgCl  in  the  last  column 
we  have  — 

Per  cent.  Os.  Per  cent.  KCl.                  AgCl  :  Salt. 

......  31.000                               84.091 

39.762  30.973                               84.102 


Mean,  84.097,  ±  .0030 

In  his  second  paper  Seubert  gives  fuller  data  relative  to  the  potassium 
osmichloride,  but  treats  it  somewhat  differently.  The  salt  was  reduced 
by  a  stream  of  hydrogen  as  before,  but  after  that  the  boat  containing  the 
Os  -{-  2KC1  was  transferred  to  a  platinum  tube,  in  which,  by  prolonged 
heating  in  the  gas,  the  potassium  chloride  was  completely  volatilized. 
The  determinations  of  4C1  as  4 AgCl  were  omitte \.  Two  series  of  data 
are  given,  as  follows  : 

*Ann.  d.  Chem.,  261,  258. 


324  THE   ATOMIC    WEIGHTS. 


Os.  Percent.  Os. 

1.1863  .4691  39-543 

.9279  -3667  39-5*9 

1.0946  .433°  39-558 

1.6055  .6351  39.558 

•4495  .1778  39-555 

.8646  .3417  39.521 

.7024  .2781  39-593 

1.2742  .504!  39-562 

1.0466  -4H1  39.566 


Mean,  39.553,  rb  .0052 

KfisClv  2KCL  Percent.  KCl. 

2.2032  .6820  3O.955 

2.0394  .6312  30.950 

2.7596  .8544  30.961 

2.4934  .77io  30.922 

2.8606  .8843  30.913 

2.8668  .5768  30.898 

1.2227  .3778  30899 


Mean,  30.931 

t/3'-C 
'130.973 


,  31.000 
Earlier  set.  '  J 


Mean  of  all  nine  determinations,  30.941,  dr  .0079 

The  single  percentage  of  osmium  in  the  earlier  memoir  is  obviously  to 
be  rejected. 

The  ratios  to  examine  are  now  as  follows : 

(i.)  Per  cent.  Os  in  Am2OsC)6,  43.459,  dr  .0036 

(2.)  6AgCl  :  Am2OsCl6  :  :  loo  :  51.283,  dr  .0099 

(3.)  4AgCl  :  K2OsCl6  :  :  IOO  :  84.097,  ±  .0030 

(4.)  Per  cent.  Os  in  K2OsCl6,  39.553,  dr  .0052 

(5.)  Per  cent.  KCl  in  K2OsCI6,  30.951,  dr  .0079 

To  reduce  these  ratios  we  have — 

Cl  =  35.179,  db  .0048  KCl    =    74.025,  ±  .0019 

K  =38.817,  rb  .0051  AgCl=  142.287,  rb  .0037 

N  =  13.935,  ±  .0021 

Hence  there  are  five  independent  values  for  osmium,  as  follows : 

From  (i) Os  =  190.111,  rb  .0300 

From  (2) "  =  190.870,  ±  .0901 

From  (3) "  =  189.928,  =b  .0371 

From  (4) "  =  188.914,  =b  .0243 

From  (5) "  =  189.571,  =b  .0928 


General  mean Os  ==  189.546,  ±  .0163 

If  0  =  16,  Os  =  190.990. 


IRIDIUM.  325 

These  figures  serve  to  fix  the  place  of  osmium  below  iridium  in  the 
periodic  classification  of  the  elements,  but  are  not  concordant  enough  to 
be  fully  satisfactory.  More  determinations  are  evidently  needed. 


IRIDIUM. 

The  only  early  determination  of  the  atomic  weight  of  iridium  was 
made  by  Berzelius,*  who  analyzed  potassium  iridichloride  by  the  same 
method  employed  with  the  platinum  and  the  osmium  salts.  The  result 
found  from  a  single  analysis  was  not  far  from  Ir  =  196.7.  This  is  now 
known  to  be  too  high.  I  have  not,  therefore,  thought  it  worth  while  to 
recalculate  Berzelius'  figures,  but  give  his  estimation  as  it  is  stated  in 
Roscoe  and  Schorlemmer's  "  Treatise  on  Chemistry." 

In  1878  the  matter  was  taken  up  by  Seubert,f  who  had  at  his  disposal 
150  grammes  of  pure  iridium.  From  this  he  prepared  the  iridichlorides 
of  ammonium  and  potassium  (NH4)2IrCl6  and  K2IrCl6,  which  salts  were 
made  the  basis  of  his  determinations.  The  potassium  salt  was  dried  by 
gentle  heating  in  a  stream  of  dry  chlorine. 

Upon  ignition  of  the  ammonium  salt  in  hydrogen,  metallic  iridium 
was  left  behind  in  white  coherent  Iamina3.  The  results  obtained  were  as 
follows  : 

Ir.  Per  cent.  Jr. 


1-3164  .5755  43725 

1.7122  .7490  43-745 

1.2657  .5536  43-739 

1.3676  .5980  43.726 

2.6496  1.1586  43-739 

2.8576  1.2489  43-705 

2.9088  1.2724  43-742 


Mean,  43-732,  ±.0035 

The  potassium  salt  was  also  analyzed  by  decomposition  in  hydrogen 
with  special  precautions.  In  the  residue  the  iridium  and  the  potassium 
chloride  were  separated  after  the  usual  method,  and  both  were  estimated. 
Eight  analyses  gave  the  following  weights  : 


KJrCl* 

C/4,  Loss. 

Ir. 

KCl. 

1.6316 

.4779 

.6507 

•5030 

2.2544 

.6600 

.8993 

•6953 

2.1290 

.6238 

.8488 

.6560 

1.8632 

•  5457 

•  743° 

.5745 

2.6898 

.7878 

1.0726 

.8291 

2-3719 

.6952 

•9459 

.7308 

2.6092 

.7641 

1.0406 

.8040 

2.5249 

•7395 

1.0070 

•  7775 

*  Poggend.  Annalen,  13,  435.     1828. 

fBer.  Deutsch.  Chem.  Gesell.,  n,  1767.     1878. 


326  THE   ATOMIC   WEIGHTS. 

Hence  we  have  the  following  percentages,  reckoned  on  the  original 
salt: 

Ir.  2KCL  Cl,. 

39.881  30.829  29.290 
39.890                              30. 842                                29.277 
39.868                              30-813  29.300 

39.876  30-835  29.289 

39.877  30-825  29.287 
39.879  3°.8n  29.310 

39.882  30.814  29.285 

39.883  30.792  29.288 

Mean,  39.880,  =fc  .0015    Mean,  30.820,  ±  .0037       Mean,  29.291,  =b  .0024 

Joly  *  studied  derivatives  of  iridium  trichloride.     The  salts  were  dried 
at  120°,  and  reduced  in  hydrogen.     With  IrCl3.3KC1.3H20  he  found  as 

follows : 

Salt.  Ir.  KCl. 

1.5950  .5881  .6803 

1.6386  -6037  .7000 

2.6276  .9689  1.1231 

These  data,  if  the  weight  of  the  salt  itself  is  considered,  give  discordant 
results,  but  the  ratio  Ir  :  3KC1 :  :  100  :  x  is  satisfactory.     The  values  of  x 

are  as  follows : 

115.677 

115.952 


Mean,  115.848,  ±  .0583 

The  ammonium  salt,  IrCl3.3NH4Cl,  gave  the  subjoined  data : 

Wt.  of  Salt.  Wt.  of  Ir.  Per  cent.  Ir. 

1.5772  .6627  42.017 

1.6056  .6742  41.990 


Mean,  42.003,  ±  .0094 

To  sum  up,  the  ratios  available  for  iridium  are  these  : 

(i.)   Per  cent.  Ir  in  Am2IrC)6,  43.732,  ±  .0035 
(2.)  Per  cent.  Ir  in  K2IrCl6,  39.880,  ±  .0015 
(3.)  Per  cent.  KCl  in  K2IrC)6,  30.820,  ±  .0037 
(4.)  Per  cent.  C14  in  K2IrCl6,  29.291,  =b  .0024 
(5.)  Per  cent.  Ir  in  Am3IrCl6,  42.003,  ±  .0094 
(6.)  Ir  :  3KC1  :  :  100  :  115.848,  ±  .0583 

The  data  for  computation  are — 

O  ==  15.879,  i  .0003  N     =  13.935,  ±  .o°21 

Cl  =  35.179,  ±  .0048  KG]  =  74.025,  ±  .0019 

K  =.  38.817,  ±  .0051  H      =  i 

*Compt.  Rend.,  no,  1131.     1890. 


PLATINUM.  327 

And  the  six  independent  values  for  the  atomic  weight  of  iridium  be- 
come— 

From  (i) Ir  =  191.935,  ±  .0300 

From  (2) "  =  191.511,  ±  .0221 

From  (3) "  =  191.604,  ±  .0485 

From  (4) "  =  191.641,  ±  .0622 

From  (5) "  =  191-833,  ±  .0641 

From  (6) ,  "  =  191.695,  ±  .0966 


General  mean Ir  •=  191.664,  ±  .0154 

If  0=16,  Ir=  193.125. 


PLATINUM. 

The  earliest  work  upon  the  atomic  weight  of  this  metal  was  done  by 
Berzelius,*  who  reduced  platinous  chloride  and  found  it  to  contain  73.3 
per  cent,  of  platinum.  Hence  Pt  =  193.155.  In  a  later  investigation  f 
he  studied  potassium  chloroplatinate,  K2PtCl6.  6.981  parts  of  this  salt, 
ignited  in  hydrogen,  lost  2.024  of  chlorine.  The  residue  consisted  of 
2.822  platinum  and  2.135  potassium  chloride.  From  these  data  we  may 
calculate  the  atomic  weight  of  platinum  in  four  ways : 

1.  From  loss  of  Cl  upon  ignition Pt  =  196.637 

2.  From  weight  of  Pt  in  residue "  =  195.897 

3.  From  weight  of  KC1  in  residue "  =  195.384 

4.  From  ratio  between  KCl  and  Pt "  =  195.690 

The  last  of  these  values  is  undoubtedly  the  best,  for  it  is  not  affected 
by  errors  due  to  the  possible  presence  of  moisture  in  the  salt  analyzed. 

The  work  done  by  Andrews  J  is  even  less  satisfactory  than  the  foregoing, 
partly  for  the  reason  that  its  full  details  seem  never  to  have  been  pub- 
lished. Andrews  dried  potassium  chloroplatinate  at  105°,  and  then 
decomposed  it  by  means  of  zinc  and  water.  The  excess  of  zinc  having 
been  dissolved  by  treatment  with  acetic  and  nitric  acids,  the  platinum 
was  collected  upon  a  filter  and  weighed,  while  the  chlorine  in  the  filtrate 
was  estimated  by  Pelouze's  method.  Three  determinations  gave  as  fol- 
lows for  the  atomic  weight  of  platinum  : 


Mean,  197.887 

Unfortunately,  Andrews  does  not  state  how  his  calculations  were  made. 

*Poggend.  Annalen,  8,  177.  1826. 
fPoggend.  Annaleti,  13,  468.  1828. 
I  British  Assoc.  Report,  1852.  Chera.  Gazette,  10, 


328  THE   ATOMIC    WEIGHTS. 

In  1881  Seubert*  published  his  determinations,  basing  them  upon 
very  pure  chloroplatinates  of  potassium  and  ammonium.  The  ammo- 
nium salt,  (NH4)2PtCl6.  was  analyzed  by  heating  in  a.stream  of  hydrogen, 
expelling  that  gas  by  a  current  of  carbon  dioxide,  and  weighing  the 
residual  metal.  In  three  experiments  the  hydrochloric  acid  formed 
during  such  a  reduction  was  collected  in  an  absorption  apparatus,  and 
estimated  by  precipitation  as  silver  chloride.  Three  series  of  experi- 
ments are  given,  representing  three  distinct  preparations,  as  follows : 

Series  I. 
Am.2PtCl6.  Pt.  Percent.  Pt, 

2.1266  .9348  43-957 

1.7880  .7858  43.948 

1.8057  .7938  43-960 

2.6876  1.1811  43-946 

4  7^74  2.0959  43-963 

2.0325  .8935  43.961 

Mean,  43.956,  =b  .002 

Series  II. 
Am^PtCl^.  Pt.  Per  cent.  Pt. 

3-046o  .3363  43-871 

2.6584  .1663  43-876 

2.3334  .0238  43-872 

1,9031  .8351  43-88: 

3.1476  .3810  43.875 

2.7054  .1871  43-889 

Mean,  43.876,  ±  .001 

Another  portion  of  this  preparation,  recrystallized  from  water,  of  1,4358 
grm.  gave  0.6311  of  platinum,  or  43.955  per  cent. 


Series  III. 

Am.PtCl,. 

Pt. 

Per  cent.  Ft. 

2.5274 

1.11*8 

43-99° 

3.2758 

1.4409 

43.986 

1.9279 

.8483 

44.001 

2.0182 

.8884 

44.020 

1.8873 

•8303 

43-994 

2.2270 

.9798 

43.996 

2.4852 

1.0936 

44.004 

2.5362 

i.i  i  66 

44.026 

3.0822 

I-356I 

43  99s 

Mean,  44.001,  ±  .003 

*Ber.  Deufcsch.  Chem.  Gesell.,  14,  865. 


PLATINUM.  329 

If  these  series  are  treated  as  independent  and  combined,  giving  each 
a  weight  as  indicated  by  its  probable  error,  and  regarding  the  single  ex- 
periment with  preparation  II  as  equal  to  one  in  the  first  series,  we  get 
a  mean  percentage  of  43.907,  ±  .0009.  On  the  other  hand,  if  we  regard 
the  twenty-two  experiments  as  all  of  equal  weight  in  one  series,  the  mean 
percentage  of  platinum  becomes  43.953,  ±  .0078.  Upon  comparing  the 
work  with  that  done  later  by  Halberstadt,  the  latter  mean  seems  the  fairer 
one  to  adopt. 

For  the  chlorine  estimations  in  the  ammonium  salt,  Seubert  gives  the 
subjoined  data.  I  add  in  the  last  column  the  weight  of  salt  proportional 
to  100  parts  of  silver  chloride. 

Am^PtCl^.                    Pt.  6AgCl.  Ratio. 

2.7054  1.1871  .                  5.2226  51.802 

2.2748  .9958  4.3758  5L9S6 

3.0822  i-356i  5-9496  S'-SoS 

Mean,  51.864,  ±  .041 

The  potassium  salt,  K.2PtCl6,  was  also  analyzed  by  ignition  in  hydro- 
gen, treatment  with  water,  and  weighing  both  the  platinum  and  the 
potassium  chloride.  The  weights  given  are  as  follows  : 


Pt.  zKCl. 

5.0283                            2.0173  i.544o 

7.0922                            2.8454  2.1793 

3.5475                            1.4217  1.0890 

3-2296                            1.2941  .9904 

35834                               1-4372  i.iooi 

4.4232  1.7746  1.3547 

4.0993  1.6444  1.2589 

4.4139  1.7713  1.3516 

Hence  we  have  these  percentages,  reckoned  on  the  original  salt 

KCl. 
30.706 
30.728 
30.698 
30.666 
30.700 
30.627 
30.710 
30.621 


Mean,  40.107,  ±  .005  Mean,  30.682,  ±  .009 

As  with  the  ammonium  salt,  three  experiments  were  made  upon  the 
potassium  compound  to  determine  the  amount  of  chlorine  (four  atoms 
in  this  case)  lost  upon  ignition  in  hydrogen.  In  the  fourth  column  I 
add  the  amount  of  K2PtCl6  corresponding  to  100  parts  of  AgCl : 


330  THE   ATOMIC    WEIGHTS. 


PL  *AgCL  Ratio. 

6.7771  2.7158  7.9725  85.006 

3.5834  L4372  4.2270  84.774 

4.4139  1.7713  5-2144  84.648 

Mean,  84.809,  ±  .071 

Halberstadt,*  like  Seubert,  studied  the  chloroplatinates  of  potassium 
and  ammonium,  and  also  the  corresponding  double  bromides  and  platinic 
bromide  as  well.  The  metal  was  estimated  partly  by  reduction  in  hy- 
drogen, as  usual,  and  partly  by  electrolysis.  Platinic  bromide  gave  the 
following  results  : 

I.  By  Reduction  in  H. 

PtBr^.  Pt.  Per  cent.  Pt. 

.6396  .2422  37.867 

1.7596  .6659  37.844 

.9178  .3476  37.873 

1.1594  .4388  37.847 

1.9608  .7420  37.842 

2.0865  .7898  37.853 

4.0796  1.5422  37-852 

6.8673  2.5985  37-8j9 

77.  By  Electrolysis. 

1.2588  .4763  37-837 

1-4937  .5649  37-819 


Mean  of  all  ten  experiments,  37.847,  ±  .0033 

The  ammonium  platinbromide,  (NH4)2PtBr6,  was  prepared  in  two 
ways,  and  five  distinct  lots  were  studied.  With  this  salt,  as  well  as  with 
those  which  follow,  the  data  are  given  in  distinct  series,  with  from  one 
to  several  experiments  in  each  group,  but  for  present  purposes  it  seems 
best  to  consolidate  the  material  and  so  put  it  in  more  manageable  form. 
The  percentages  of  platinum  and  weights  found  are  as  follows  : 

/.  By  Reduction  in  H. 

Pt.  Percent.  Pt. 


'  .6272 

.1719 

27.408 

.0438 

.2865 

27.447 

.1724 

.3215 

27.422 

1  .4862 

.4076 

27.426 

.0811 

.2966 

27.435 

.  .3383 

.3672 

27.437 

*Ber.  Deutsch.  Chem.  Gesell.,  17,  2962.     1884. 


PLATINUM. 


331 


PL 
.2769 
.3269 
.3611 
.6159 
.3668 

.4899 
1.1427 

•  3250 
.6591 
.6940 

.4705 
.6316 
.8245 

I-3329 
.4210 
•5594 
•5751 


Per  cent.  PL 
27.426 
27.390 

27-393 
27.402 

27-45* 
27.431 
27.441 
27.460 
27.459 
27.438 

27-439 
27-444 
27.435 
27.430 

27.449 
27-457 
27.465 


II.  By  Electrolysis. 

.4272  27.409 

.4397  27.392 

.8569  27.439 

.3180  27.386 

.7081  27.427 

.2809  27.456 

.4591  27.418 

.4591  27.418 

•4397  27.392 

Mean  of  all  thirty-two  experiments,  27.429,  ±  .0027 


With  potassium  platinbromide  Halberstadt  found  as  follows : 


f  2.5549 
|  2.6323 

•j  2.93 '5 

3-4463 

1^4.0081 

3-9554 
2.0794 

2.1735 
2.3099 

1.4085 
2.6166 
2.6729 


PL 

.6630 
.6831 
.7598 
.8939 
1.0404 
1.0266 
.5388 

.5635 
.5986 

•3645 
.6772 

.6923 


/.  By  Reduction  in  H. 


2KBr. 

.8071 
.8318 

.9259 
1.0895 
1-2653 
1.2495 

.6558 
.6849 
.7297 

.4446 
.8279 
.8469 


Per  cent.  PL        Per  cent.  KBr. 


25.940 
25.947 
25.910 
25-938 
25.957 
25.954 
25.911 
25.926 
25.914 
25.880 
25.881 
25.900 


3L590 
31-599 
31-584 
3L6I3 
31.568 

31-589 
3L538 
31.5" 
3L590 

3L565 
31.640 
31.684 


332 


THE   ATOMIC    WEIGHTS. 


$:2/^r6. 

Pt. 

sKBr. 

Percent.  Pt. 

2.  21  10 

•5726 

.6997 

25.898 

3.1642 

.8188 

•9983 

1.9080 

1.6754 

•4947 
•4341 

.6025 
.5286 

25.927 
25-915 

1.3148 

•  3403 

.4160 

25.882 

L5543 

.4025 

.4911 

25-895 

By  Electrolysis. 

Per  cent.  KBr. 
3L647 
3L550 
31-577 
3L550 
3^.640 

31.596 

Mean  of  eighteen  experiments,  25.915,  ±  .0040     31.591,  ±  .0068 

For  ammonium  platinchloride  Halberstadt  gives  the  following  data : 
/.  By  Reduction  in  H. 

Pt. 

.4.662 

.6087 

.6617 
1.0227 

.6059 

.7638 
1.2068 
1.4019 

2-4035 

J-532I 


Per  cent.  Pt. 

43-964 
43.962 


43.956 
43.880 
43.906 
44.011 
43-971 
43-984 
43.951 


•9474 
1.1069 
1.5101 

•5345 
1-6035 

1.9271 
1.1046 
1.4179 


//.  By  Electrolysis. 
.4161 
.4865 
.6634 
.2347 
.7044 

.8459 
.4858 
•6233 


43.920 
43.951 
43.930 

43-910 
43-928 

43.894 
43-979 
43-959 


Mean  of  eighteen  experiments,  43.943,  ±  .0054 
Seubert  found,  43.953,  ±  .0078 

General  mean,  43.946,  ±  .0044 

For  potassium  platinchloride  Halberstadt's  data  are— 
/.  By  Reduction  in  H. 


K.PtCl,. 

Pt. 

2KCI. 

Percent.  Pt. 

Per  cent.  KCL 

f  1.6407 

.6574 

.5029 

40.069 

30-651 

1  1-9352 

{' 

•7757 

•5921 

40.084 

30.600 

L5793 

.6334 

.4836 

40.106 

30.621 

1.6446 

•6595 

.5049 

40.  101 

.   30.700 

1.0225 
2.4046 

.4102 
.9641 

•3133 

.7388 

40.117 
40.094 

30.640 
30.724 

f  5.8344 

2.3412 

1.7005 

40.127 

30.688 

(7.1732 

2.8776 

2.1998 

40.116 

30.666 

PLATINUM.  333 

77.  By  Electrolysis. 

PL  2KCL           Per  cent.  Pt.       Per  cent.  KCl. 

1.2354                  .4953  .3792  40.092  30.695 

2.5754                1.0318  .7898  40.063  30.667 

L0933                 .4387  .3355  40.126  30.668 

1.3560                 .5438  .4167  40.103  30.730 

L7345                 .6956  .5298  40.104  30.545 

2.0054                 .8038  .6147  40.081  30.652 

2.0666                 .8291  .6356  40.117  3O.755 

1.2759                 .5"8  .3908  40.112  30.629 

1.9376                 .7763  .5927  40.065  30.589 

2.3972                 .9608  .7355  40.080  30.681 

1.2.7249                1.0929  .8364  40.108  30.691 


Mean  of  nineteen  experiments,  40.098,  rb  .0031     30.663,  ±  .0080 
Seubert  found,  40. 107,  ±  .0050     30.682,  ±  .0090 

General  mean ,.40.101,  d=  .0026     30.671,  ±  .0060 

The  work  of  Dittmar  and  M'Arthur*  on  the  atomic  weight  of  platinum 
is  difficult  to  discuss  and  essentially  unsatisfactory.  They  investigated 
potassium  platinchloride,  and  came  to  the  conclusion  that  it  contains 
traces  of  hydroxyl  replacing  chlorine  and  also  hydrogen  replacing 
potassium.  It  is  also  liable,  they  think,  to  carry  small  quantities  of 
potassium  chloride.  In  their  determinations,  which  involve  corrections 
indicated  by  the  foregoing  considerations,  they  are  not  sufficiently  ex- 
plicit, and  give  none  of  their  actual  weighings.  They  attempt,  however, 
to  fix  the  ratio  2KC1 :  Pt,  and  after  a  number  of  discordant,  generally 
high  results,  they  give  the  following  data  for  the  atomic  weight  of  plati- 
num based  upon  the  assumption  that  2KC1  =  149.182 : 

195.54 
195.48 
195.60 
195.37 


Mean,  195.50,  ±.0330. 

Dittmar  and  M'Arthur  also  discuss  Seubert's  determinations,  seeking 
to  show  that  the  latter  also,  properly  treated,  lead  to  a  value  nearer  to 
195.5  than  to  195.  Seubert  at  once  replied  to  them,f  pointing  out  that 
the  concordance  between  his  determinations  by  very  different  methods 
(a  concordance  verified  by  Halberstadt's  investigation)  precluded  the 
existence  of  errors  due  to  impurities  such  as  Dittmar  and  M'Arthur 
assumed. 

*  Trans.  Roy.  Soc.  Edinburgh,  33,  561.     1887. 
tBer.  Deutsch.  Chem.  Gesell.,  21,  2179.     1888. 


334  THE   ATOMIC    WEIGHTS. 

The  ratios  from  which  to  compute  the  atomic  weight  of  platinum  are 
now  as  follows,  rejecting  the  work  of  Berzelius  and  of  Andrews : 

(i.)   Percentage  of  Pt  in  ammonium  platinchloride,  43.946,  ±  .0044 
(2.)   Percentage  of  Pt  in  ammonium  platinbromide,  27.429,  db  .0027 
(3.)  Percentage  of  Pt  in  potassium  platinchloride,  40.101,  ±  .0026 
(4.)   Percentage  of  Pt  in  potassium  platinbromide,  25.915,  ±  .0040 
(5.)   Percentage  of  Pt  in  platinic  bromide,  37.847,  =b  .0033 
(6.)  Percentage  of  KC1  in  potassium  platinchloride,  30.671,  ±  .0060 
(7.)   Percentage  of  KBr  in  potassium  platinbromide,  31.591,  =b  .0068 
(8.)  6AgCl  :  Am2PtCl6  :  :  100  :  51.864,  rb  .041 
(9.)  4AgCl  :  K2PtCl6  :  :  loo  :  84.809,  ±  .071 
(10.)   2KC1  :  Pt  :  :  149.182  :  195.50,  dr  .033 

Computing  with  the  subjoined  atomic  and  molecular  weights — 
Cl  =  35.179,  ±  .0048  KC1  =  74.025,  rb  .0019 

Br  =  79.344,  ±  .0062  KBr  =  118.200,  rb  .0073 

K  =  38.817,  rb  .0051       .  AgCl  =  142.287,  ±  .0037 

N  =  13.935,  ±  .0021 

we  have  the  following  ten  values  for  platinum  : 

From  (i) Pt  =  193.603,  rb  .0336 

From  (2) "=  193.493,  ±.0248 

From  (3) "  =  193.283,  =b  .0254 

From  (4) "  =  193.684,  db  .0344 

From  (5) "  =  193.261,  rfc  .0248 

From  (6) "  =  193  938,  rb  .0746 

From  (7) "  =  194-538,  =b  . 1276 

From  (8) "  =  195.836,  rb  .3515 

From  (9) "  =  193.980,  ±  .4054 

From  (10) "  =  194.017,  db  .0331 

General  mean  . Pi  =  193.443,  ±  .0114 

If  0  =  16,  Pt  =  194.917. 

Of  these  ten  values  the  first  five  are  obviously  the  most  trustworthy. 
Their  general  mean  is  Pt  =  193.414,  ±  .0124 ;  or,  if  0  =  16,  Pt  =  194.888. 
This  result  is  preferable  to  the  mean  of  all,  even  though  the  latter  varies 
little  from  it.  The  five  high  values  carry  very  little  weight  because  of 
their  larger  probable  errors. 


CERIUM.  335 


CERIUM. 

Although  cerium  was  discovered  almost  at  the  beginning  of  the  present 
century,  its  atomic  weight  was  not  properly  determined  until  after  the 
discovery  of  lanthanum  and  didymium  by  Mosander.  In  1842  the  in- 
vestigation was  undertaken  by  Beringer,*  who  employed  several  methods. 
His  cerium  salts,  however,  were  all  rose-colored,  and  therefore  were  not 
wholly  free  from  didymium ;  and  his  results  are  further  affected  by  a 
negligence  on  his  part  to  fully  describe  his  analytical  processes. 

First,  a  neutral  solution  of  cerium  chloride  was  prepared  by  dissolving 
the  carbonate  in  hydrochloric  acid.  This  gave  weights  of  eerie  oxide  and 
silver  chloride  as  follows.  The  third  column  shows  the  amount  of  CeO2 
proportional  to  100  parts  of  AgCl : 

CeO2.  AgCl.  Ratio. 

•  5755  grm.  1.419  grm.  4O-557 

.6715     "  1.6595  "  40.464 

1.1300     "  2.786     "  40.560 

.5366     "  i.33'6  "  40.297 

Mean,  40.469,  ±  .0415 

The  analysis  of  the  dry  cerium  sulphate  gave  results  as  follows.  In 
a  fourth  column  I  show  the  amount  of  Ce02  proportional  to  100  parts  of 
BaS04 : 

Sulphate.  CeO^.  BaSO±  Ratio. 

1.379  grm.  .8495  grm.  1.711  grm.  49.649 

1.276     "  .7875     "  1.580     "  49.836 

1.246     "  .7690     "  1.543     "  49.838 

1.553     "  .9595     "  1.921     "  49.948 

Mean,  49.819,  ±  .042 

Beringer  also  gives  a  single  analysis  of  the  formate  and  the  results  of 
one  conversion  of  the  sulphide  into  oxide.  -The  figures  are,  however, 
not  valuable  enough  to  cite. 

The  foregoing  data  involve  one  variation  from  Beringer's  paper. 
Where  I  put  Ce02  as  found  he  puts  Ce2Os.  The  latter  is  plainly  inad- 
missible, although  the  atomic  weights  calculated  from  it  agree  curiously 
well  with  some  other  determinations.  Obviously,  the  presence  of  didym- 
ium in  the  salts  analyzed  tends  to  raise  the  apparent  atomic  weight  of 
cerium. 

Shortly  after  Beringer,  Hermann  f  published  the  results  of  one  experi- 
ment. 23.532  grm.  of  anhydrous  cerium  sulphate  gave  29.160  grm.  of 
BaS04.  Hence  100  parts  of  the  sulphate  correspond  to  123.926  of  BaS04. 

*Ann.  Chem.  Pharm.,42,  134.     1842. 

t  Journ.  fur  Prakt.  Chem.,  30,  185.     1843. 


336  THE    ATOMIC   WEIGHTS. 

In  1848  similar  figures  were  published  by  Marignac,*  who  found  the 
following  amounts  of  BaS04  proportional  to  100  of  dry  cerium  sulphate : 


Mean,  122.40,  ±  .138 

If  we  give  Hermann's  single  result  the  weight  of  one  experiment  in 
this  series,  and  combine,  we  get  a  mean  value  of  122.856,  ±  .130. 

Still  another  method  was  employed  by  Marignac.  A  definite  mixture 
was  made  of  solutions  of  cerium  sulphate  and  barium  chloride.  To  this 
were  added,  volumetrically,  solutions  of  each  salt  successively,  until 
equilibrium  was  attained.  The  figures  published  give  maxima  and 
minima  for  the  BaCl2  proportional  to  each  lot  of  Ce.2(SO4)3.  In  another 
column,  using  the  mean  value  for  BaCl2  in  each  case,  I  put  the  ratio 
between  100  parts  of  this  salt  and  the  equivalent  quantity  of  sulphate. 
The  latter  compound  was  several  times  recrystallized  : 


BaClv  Ratio. 

First  crystallization  ......    ii.ongrm.      11.990  —  12.050  grm.     91.606 

First  crystallization.  :  ____    13.194     "        i4-365  —  T4-425     "        91-657 


Second  crystallization..  .  . 

13.961 

15.225  —  15.285 

91.518 

Second  crystallization..  .  . 

12.627      " 

13.761  —  13.821      " 

9L559 

Second  crystallization..  .  . 

11.915      " 

12.970  —  13.030     " 

91-654 

Third  crystallization  

14.888     <« 

16.223  —  16.283     " 

91.602 

Third  crystallization  

14.113     " 

I5.383  —  I5-423     " 

9L755 

Fourth  crystallization..  .  . 

13.111      " 

14.270—14.330     " 

91.685 

Fourth  crystallization 13.970  J5-223 — 15.283     "        91.588 

Mean,  91.625,  ±  .016 

Omitting  the  valueless  experiments  of  Kjerulf,f  we  come  next  to  the 
figures  published  by  Bunsen  and  Jegel  J  in  1858.  From  the  air-dried 
sulphate  of  cerium  the  metal  was  precipitated  as  oxalate,  which,  ignited, 
gave  Ce02.  In  the  filtrate  from  the  oxalate  the  sulphuric  acid  was  esti- 
mated as  BaSO4 : 

1.5726  grm.  sulphate  gave  .7899  grm.  CeO2  and  1.6185  Srm-  BaSO4. 
1.6967  "  .8504  "  1.7500         " 

Hence,  for  100  parts  BaSO4,  the  CeOa  is  as  follows : 

48.804 
48.575 


Mean,  48.689,  d=  .077 


*Arch.  Sci.  Phys.  et  Nat.  (i),  8,  273.     1848. 

t  Ann.  Chem.  Pharra.,  87,  12. 

J  Ann.  Chem.  Pharni.,  105,  45.     1858. 


CERIUM.  337 

One  experiment  was  also  made  upon  the  oxalate  : 


•353°  Srm-  oxalate  gave  .1913  CeO2  and  .0506  H2O. 

Hence,  in  the  dry  salt,  we  have  63.261  per  cent,  of  CeO2. 

In  each  sample  of  Ce02  the  excess  of  oxygen  over  Ce203  was  estimated 
by  an  iodometric  titration  ;  but  the  data  thus  obtained  need  not  be  fur- 
ther considered. 

In  two  papers  by  Rammelsberg*  data  are  given  for  the  atomic  weight 
of  cerium,  as  follows.  In  the  earlier  paper  cerium  sulphate  was  analyzed, 
the  cerium  being  thrown  down  by  caustic  potash,  and  the  acid  precipi- 
tated from  the  nitrate  as  barium  sulphate  : 

.413  grm.  Ce2(SO4)3  gave  .244  grm.  Ce02  and  .513  grm.  BaSO4. 

Hence  100  BaSO4  =  47.563  Ce02,  a  value  which  may  be  combined  with 
others,  thus  ;  this  figure  being  assigned  a  weight  equal  to  one  experi- 
ment in  Bunsen's  series  : 

Beringer  ...............................   49.819,  ±  .042 

Kunsen  and  Jegel  .........................   48.689,  ±  .077 

Rammelsberg  .....  .......................   47-5^3>  -t-  .  108 


General  mean 49.360,  =b  .035 

It  should  be  noted  here  that  this  mean  is  somewhat  arbitrary,  since 
Bunsen  and  Rammelsberg's  cerium  salts  were  undoubtedly  freer  from 
didymium  than  the  material  studied  by  Beringer, 

In  his  later  paper  Rammelsberg  gives  these  figures  concerning  cerium 
oxalate.  One  hundred  parts  gave  10.43  of  carbon  and  21.73  of  water. 
Hence  the  dry  salt  should  yield  48.862  per  cent,  of  CO2,  whence  Ce  = 
137.14. 

In  all  of  the  foregoing  experiments  the  eerie  oxide  was  somewhat  col- 
ored, the  tint  ranging  from  one  shade  to  another  of  light  brown  according 
to  the  amount  of  didymium  present.  Still,  at  the  best,  a  color  remained, 
which  was  supposed  to  be  characteristic  of  the  oxide  itself.  In  1868, 
however,  some  experiments  of  Dr.  C.  Wolff  were  posthumously  made 
public,  which  went  to  show  that  pure  ceroso-ceric  oxide  is  white,  and 
that  all  samples  previously  studied  were  contaminated  with  some  other 
earth,  not  necessarily  didymium  but  possibly  a  new  substance,  the  re- 
moval of  which  tended  to  lower  the  apparent  atomic  weight  of  cerium 
very  perceptibly. 

Cerium  sulphate  was  recrystallized  at  least  ten  times.  Even  after 
twenty  recrystallizations  it  still  showed  spectroscopic  traces  of  didymium. 
The  water  contained  in  each  sample  of  the  salt  was  cautiously  estimated, 
and  the  cerium  was  thrown  down  by  boiling  concentrated  solutions  of 

*  Poggend.  Annalen,  55,  65  ;  108,  44. 

t  Amer.  Journ.  Science  and  Arts  (2),  46,  53. 


338 


THE    ATOMIC   WEIGHTS. 


oxalic  acid.  The  resulting  oxalate  was  ignited  with  great  care.  I  de- 
duce from  the  weighings  the  percentage  of  Ce02  given  by  the  anhydrous 
sulphate  : 

CeO.^ 

.76305  grin. 

.7377      « 

.70665    " 


Sulphate. 
1.4542  grm. 
1.4104    " 
1.35027  " 


Water. 


.  19419  grrn. 
.1898      " 
.1820      " 


Percent. 
60.559 
60.437 
60.487 


Mean,  60.494 


After  the  foregoing  experiments  the  sulphate  was  further  purified  by 
solution  in  nitric  acid  and  pouring  into  a  large  quantity  of  boiling  water. 
The  precipitate  was  converted  into  sulphate  and  analyzed  as  before  : 

Sulphate.  Water.  CeO.>. 

L4327  grm-  .2733  grm-  -69925  grm. 

1.5056    "  .2775    "  .7405       " 

1.44045  "  .2710    "  .7052      " 


Per  cent.  CeO.2. 
60.311 
60.296 
60.300 


Mean,  60.302 

From  another  purification  the  following  weights  were  obtained : 

1.4684  grm.      .1880  grm.      .7717  grm.      60.270  per  cent. 

A  last  purification  gave  a  still  lower  percentage : 

t.3756  grm.      .1832  grm.      .7186  grm.      60.265  per  cent. 

The  last  oxide  was  perfectly  white,  and  was  spectroscopically  free  from 
didymium.  In  each  case  the  Ce02  was  titrated  iodometrically  for  its 
excess  of  oxygen.  It  will  be  noticed  that  in  the  successive  series  of  de- 
terminations the  percentage  of  Ce02  steadily  and  strikingly  diminishes 
to  an  extent  for  which  no  ordinary  impurity  of  didymium  can  account. 
The  death  of  Dr.  Wolf  interrupted  the  investigation,  the  results  of  which 
were  edited  and  published  by  Professor  F.  A.  Genth. 

In  the  light  of  more  recent  evidence,  little  weight  can  be  given  to  these 
observations.  All  the  experiments,  taken  equally,  give  a  mean  percent- 
age of  Ce02  from  Ce2(S04)3  of  60.366,  ±  .0308.  This  mean  has  obviously 
little  or  no  real  significance. 

The  experiments  of  Wolf  attracted  little  attention,  except  from  Wing,* 
who  partially  verified  certain  aspects  of  them.  This  chemist,  incidentally 
to  other  researches,  purified  some  cerium  sulphate  after  the  method  of 
Wolf,  and  made  two  similar  analyses  of  it,  as  follows  : 

Sulphate.  Water.  CeO.2.  Percent.  CeO.2. 

1.2885  grm.  .1707  grm.  .6732  grm.  60.225 

1.4090     "  .1857     "  .7372     "  60.263 

Mean,  60  244 


*  Am.  Journ.  Sci.  (2),  49,  358.     1870. 


CERIUM.  339 

The  cerio  oxide  in  this  case  was  perfectly  white.  The  cerium  oxalate 
which  yielded  it  was  precipitated  boiling  by  a  boiling  concentrated  solu- 
tion of  oxalic  acid.  The  precipitate  stood  twenty-four  hours  before 
filtering. 

In  1875  Buehrig's  *  paper  upon  the  atomic  weight  of  cerium  was  issued. 
He  first  studied  the  sulphate,  which,  after  eight  crystallizations,  still 
retained  traces  of  free  sulphuric  acid.  He  found,  furthermore,  that  the 
salt  obstinately  retained  traces  of  water,  which  could  not  be  wholly  ex- 
pelled by  heat  without  partial  decomposition  of  the  material.  These 
sources  of  error  probably  affect  all  the  previously  cited  series  of  experi- 
ments, although,  in  the  case  of  Wolf's  work,  it  is  doubtful  whether  they 
could  have  influenced  the  atomic  weight  of  cerium  by  more  than  one  or 
two  tenths  of  a  unit.  Buehrig  also  found,  as  Marignac  had  earlier  shown, 
that  upon  precipitation  of  cerium  sulphate  with  barium  chloride  the 
barium  sulphate  invariably  carried  down  traces  of  cerium.  Furthermore, 
the  eerie  oxide  from  the  filtrate  always  contained  barium.  For  these 
reasons  the  sulphate  was  abandoned,  and  the  atomic  weight  determina- 
tions of  Buehrig  were  made  with  air-dried  oxalate.  This  salt  was  placed 
in  a  series  of  platinum  boats  in  a  combustion  tube  behind  copper  oxide. 
It  was  then  burned  in  a  stream  of  pure,  dry  oxygen,  and  the  carbonic 
acid  and  water  were  collected  after'the  usual  method.  Ten  experiments 
were  made;  in  all  of  them  the  above-named  products  were  estimated, 
and  in  five  analyses  the  resulting  eerie  oxide  was  also  weighed.  By  de- 
ducting the  water  found  from  the  weight  of  the  air-dried  oxalate,  the 
weight  of  the  anhydrous  oxalate  is  obtained,  and  the  percentages  of  its 
constituents  are  easily  determined.  In  weighing,  the  articles  weighed 
were  always  counterpoised  with  similar  materials.  The  following  weights 
were  found : 

Oxalate.  Water.  CO2.  CeO.z. 

9.8541  grm.  2.i987grm.  3.6942  grm 

9.5368  "  2.1269  "  3-5752     " 

9.2956  "  2.0735  "  3.4845     " 

10.0495  "  2.2364  "  3-77°4     " 

10.8249  "  2.4145  "  4.0586     "  

9.3679  "  2.0907  "  3-5118     "  4-6150  grm. 

9.7646  "  2.1769  "  3.6616     "  4.8133      " 

9.9026  "  2.2073  "  3.7139  s  "  4-8824      " 

9.9376  "  2.2170  "  3.7251      "  4-8971       " 

9.5324  "  2.1267  "  3-5735     "  4-6974      " 


These  figures  give  us  the  following  percentages  for  C02  and  Ce02  in  the 
anhydrous  oxalate : 

*  Journ.  fi'ir  Prakt.  Chem.,  120,  222.     1875. 


340  THE    ATOMIC    WEIGHTS, 

CO.r  CeO,. 

48.256  

48.249  

48.248  

48.257  

48.257 

48.258  63417 
48.257  63.436 
48.262  63.446 

48.249  63.429 
48.253  63.430 


Mean,  48.2546  ±  .001  Mean,  63.4316,  =b  .0032 

These  results  could  not  be  appreciably  affected  by  combination  with 
the  single  oxalate  experiments  of  Jegel  and  of  Rarnmelsberg,  and  the 
latter  may  therefore  be  ignored. 

Robinson's  work,  published  in  1884,*  was  based  upon  pure  cerium 
chloride,  prepared  by  heating  dry  cerium  oxalate  in  a  stream  of  dry, 
gaseous  hydrochloric  acid.  This  compound  was  titrated  with  standard 
solutions  of  pure  silver,  prepared  according  to  Stas,  and  these  were 
weighed,  not  measured.  In  the  third  column  I  give  the  ratio  between 
CeCl3  and  100  parts  of  silver  : 

CeCl3.  Ag.  Ratio. 

5.5361  7.26630  76.189 

6.0791  7-98377  76  172 

6.4761  8.50626  76.133 

6.98825  9.18029  76.122 

6.6873  8.78015  76.164 

7.0077  9.20156  76.158 

6.9600  9-r393°  76.150 


Mean 

Reduced  to  a  vacuum  this  becomes  76.167. 

In  a  later  paper,  f  Robinson  discusses  the  color  of  eerie  oxide,  and 
criticises  the  work  of  Wolf.  He  shows  that  the  pure  oxide  is  not  white, 
and  makes  it  appear  probable  that  Wolf's  materials  were  contaminated 
with  compounds  of  lanthanum.  He  also  urges  that  Wolf's  cerium  sul- 
phate could  not  have  been  absolutely  definite,  because  of  defects  in  the 
method  by  which  it  was  dehydrated. 

Brauner,J  in  1885,  investigated  cerium  sulphate  with  extreme  care, 
and  appears  to  have  obtained  material  free  from  all  other  earths  and 
absolutely  homogeneous.  The  anhydrous  salt  was  calcined  with  all 

*  Chemical  News,  50,  251.     Nov.  28,  1884.     Proc.  Roy.  Soc.,  37,  150. 
t  Chemical  News,  54,  229.     1886. 
t  Sitzungs.  Wien.  Akad.,  Bd.  92.    July,  1885. 


CERIUM.  341 

necessary  precautions,  and  the  data  obtained,  reduced  to  a  vacuum,  were 
as  follows : 

Ce.2(SO±\.                           CeOr  Percent.  CeO2. 

2.16769                            1.31296  60.5693 

2.43030                            1.47205  60.5707 

2.07820                            1.25860  60.5620 

2.21206                            1.33989  60.5721 

1.28448                              .77845  60.6043 

1.95540                            1.18436  60.5687 

2.46486                             1.49290  60.5673 

2.04181                              1.23733  6o-5997 

2.17714                              1.31878  60.5739 

2.09138                              1.26654  60.5605 

2.21401                              1.34139  60.5863 

2.44947                              1.48367  60.5711 

2.22977                              1.35073  60.5771 

2.73662                              1.65699  60.5486 

2.62614                              1.59050  60.5642 

1.67544                              1.01470  60.5632 

1.57655                                -95540  60.6007 

2.72882                              1.65256  60.5600 

2.10455                              1.27476  60.5716 

2-IO735                             1.27698  60.5965 

2-43557                              I-4751?  60.5692 

3.01369                              1.82524  60.5649 

4.97694                             3.0I372  60.5537 

Mean,  60  5729,  ±  .0021 

This  mean  completely  outweighs  the  work  done  by  Wolf  and  Wing, 
so  that  upon  combination  the  latter  practically  vanish.  Wing's  mean  is 
arbitrarily  given  equal  weight  with  Wolf's,  and  the  combination  is  as 
follows : 

Wolf. 60.366,   ±  .0308 

Wing 60. 244,    =b  .0308 

Brauner 60.5729,  ±  .0021 


General  mean 60.566,     d=  .0021 

In  1895  several  papers  upon  the  cerite  earths  were  published  by  Schutz- 
^nberger.*  In  the  first  of  these  a  single  determination  of  atomic  weight 
is  given.  Pure  Ce0.2,  of  a  yellowish  white  color,  was  converted  into  sul- 
phate, which  was  dried  in  a  current  of  dry  air  at  440°.  This  salt,  dis- 
solved in  water,  was  poured  into  a  hot  solution  of  caustic  soda,  made 
from  sodium,  and,  after  filtration  and  washing,  the  filtrate,  acidulated 
with  hydrochloric  acid,  was  precipitated  with  barium  chloride.  The 
trace  of  sulphuric  acid  retained  by  the  cerium  hydroxide  was  recovered 
by  re-solution  and  a  second  precipitation,  and  added  to  the  main  amount. 

*  Compt.  Rend.,  120,  pp.  663,  962,  and  1143.     1895. 


342  THE    ATOMIC   WEIGHTS. 

100  parts  of  Ce,(S04)3  gave  123.30  of  BaS04.  This  may  be  assigned  equal 
weight  with  one  experiment  in  Marignac's  series,  giving  the  following 
combination : 

Hermann 123  926,  ±  .238 

Marignac 122.40,     ±.138 

Schutzenherger 123.30,     ±  .238 


General  mean  .....................    122.958,  ±  .  1  139 

Schutzenberger,  criticising  Brauner's  work,  claims  that  the  latter  was 
affected  by  a  loss  of  oxygen  during  the  calcination  of  the  cerium  dioxide. 

In  his  second  and  third  papers  Schutzenberger  describes  the  results 
obtained  upon  the  fractional  crystallization  of  cerium  sulphate.  Prepa- 
rations were  thus  made  yielding  oxides  of  various  colors  —  canary  yellow, 
rose,  yellowish  rose,  reddish,  and  brownish  red.  These  oxides,  by  syn- 
thesis of  sulphates,  the  barium-sulphate  method,  etc.,  gave  varying  values 
for  the  atomic  weight  of  cerium,  ranging  from  135.7  to  143.3.  Schutzen- 
berger therefore  infers  that  cerium  oxide  from  cerite  contains  small 
quantities  of  another  earth  of  lower  molecular  weight  ;  but  the  results  as 
given  are  not  sufficiently  detailed  to  be  conclusive.  The  third  paper  is 
essentially  a  continuation  of  the  second,  with  reference  to  the  didymiums. 

Schutzenberger's  papers  were  promptly  followed  by  one  from  Brauner,* 
who  claims  priority  in  the  matter  of  fractio  nation,  and  gives  some  new 
data,  the  latter  tending  to  show  that  cerium  oxide  is  a  mixture  of  at  least 
two  earths.  One  of  these,  of  a  dark  salmon  color,  he  ascribes  to  a  new 
element,  "  meta-cerium."  The  other  he  calls  cerium,  and  gives  for  it  a 
preliminary  atomic  weight  determination.  The  pure  oxalate,  by  Gibbsy 
method,  gave  46.934  per  cent,  of  Ce02,  and,  on  titration  with  potassium 
permanganate,  29.503  and  29.506  per  cent,  of  C2O3.  Hence  Ce  =  138.799. 
In  mean,  this  ratio  may  be  written— 

3C203  :  2Ce02  :  :  29.5045  :  46-934, 

and  to  each  of  its  numerical  terms  we  may  roughly  assign  the  probable 
error  ±  .001.  This  is  derived  from  the  average  of  the  two  titrations,  and 
is  altogether  arbitrary. 

The  ratios,  good  and  bad,  for  cerium  now  are  — 

(i.)  Ce2(SO4\s  :  3BaSO4  :  :  100  :  122.958,  d=  .1139 

(2.)  3BaSO4  :  2CeO2  :  :  100  :  49-36o,  ±  .035 

(3.)  3BaCl2  :  Ce2(S04)3  :  :  loo  :  91.625,  ±  .016 

(4.)  3AgCl  :  CeO2  :  :  loo  :  40.469,  ±  .0415 

(5.)   Percentage  CeO2  from  Ce2(SO4)3,  60.566,  ±  .0021 

(6.)   Percentage  CeO2  from  Ce2(C2O4>)3,  63.4316,  +  .0032 

(7.)  Percentage  CO2  from  Ce2(C2O4)3,  48.2546,  =b  .001. 

(8.)  3Ag  :  CeCl3  :  :  IOO  :  76.167,  ±  .0065 

(9-)  3C2°3  :  2Ce°2  :  :  29.5045,  ±  .001  :  46.934,  ±  -ooi 


*Chem.  News,  71,  283. 


CERIUM.  343 

To  reduce  these  ratios  we  have  — 

O  =      I5.879,:t.OOO3  C      =      II.92O,   ±  .OOO4 

Cl       =    35.179,  d=  .0048  S    =    31.828,  zb  .0015 

Ag      =  107.108,  dz  .0031  Ba  =  136.392,  ±  .0086 

i42.287,  ±.0037 


From  the  ratios,  with  these  intermediate  data,  we  can  get  two  values 
for  the  molecular  weight  of  Ce2(S04)3,  and  five  for  that  of  Ce02.  For 
cerium  sulphate  we  have  — 

From  (i)  ...................   Ce2(SO4)3  =  565.404,  ±  .  1670 

From  (3)  ...................  "          =  568.304,  db  .  1054 

General  mean  .........    Cez(SO4)3  =  567.478,  ±  .0891 

Hence  Ce  ==  140.723,  ±  .0451. 
For  eerie  oxide  the  values  are  — 

From  (2)  ......  '  .................  CeO2—  171.577,  ±  .1218 

From  (4)  ...........  .  ...........      "       =  172.746,^.1772 

From  (5)  .......................      "     =r  170.879,  ±  .0115 

From  (6)  .......................      "     =172.125,^.0177, 

From  (9)  ......................      "     =  170.557,  ±  .0076 

General  mean  .............  CeO2  =  170.827,  ±  .0060 

And  Ce  =  139.069,  ±.0061. 

For  cerium  itself,  four  independent  values  are  now  calculable,  as 
follows  : 

From  molecular  weight  of  sulphate.  .  .  Ce  =  140.723,  ±  .0451 

From  molecular  weight  of  dioxide  ...  "  =  139.069,  rb  .0061 

From  ratio  (8)  ....................  "  =  139.206,  ±  .0263 

From  ratio  (7)  ...............  .....  "  =  140.516,  ±  .0047 

General  mean  ...............  Ce  =  140.  1  13,  =b  .0036 

If  0  =  16,  Ce  =  141.181. 

It  must  be  admitted  that  this  combination  is  of  very  questionable 
utility.  Its  component  means  vary  too  widely  from  each  other,  and  in- 
volve too  many  uncertainties.  Furthermore,  Schutzenberger  and  Brau- 
ner  both  impugn  the  homogeneity  of  the  supposed  element,  as  it  has 
hitherto  been  recognized.  Even  if  no  "  meta-elements  "  are  involved  in 
the  discussion,  it  seems  clear,  on  chemical  grounds,  that  the  two  lower 
values  are  really  preferable  to  the  two  higher,  and  that  ratio  (7)  receives 
excessive  weight.  The  general  mean  obtained  is  probably  a  full  unit  too 
high.  The  value  139.1  is  perhaps  nearly  correct. 


344  THE    ATOMIC    WEIGHTS. 


LANTHANUM. 

Leaving  out  of  account  the  work  of  Mosander.  and  the  valueless  ex- 
periments of  Choubine,  we  may  consider  the  estimates  of  the  atomic 
weight  of  lanthanum  which  are  due  to  Hermann,  Rammelsberg,  Marig- 
nac,  Czudnowicz,  Holzmann,  Zschiesche,  Erk,  Cleve,  Brauner,  Bauer, 
and  Bettendorff. 

From  Rammelsberg*  we  have  but  one  analysis.  .700  grm.  of  lantha- 
num sulphate  gave  .883  grm.  of  barium  sulphate.  Hence  100  parts  of 
BaS04  are  equivalent  to  79.276  of  La2(S04)3. 

Marignac.f  working  also  with  the  sulphate  of  lanthanum,  employed 
two  methods.  First,  the  salt  in  solution  was  mixed  with  a  slight  excess 
of  barium  chloride.  The  resulting  barium  sulphate  was  filtered  off  and 
weighed;  but,  as  it  contained  some  occluded  lanthanum  compounds,  its 
weight  was  too  high.  In  the  filtrate  the  excess  of  barium  was  estimated, 
also  as  sulphate.  This  last  weight  of  sulphate,  deducted  from  the  total 
sulphate  which  the  whole  amount  of  barium  chloride  could  form,  gave 
the  sulphate  actually  proportional  to  the  lanthanum  compound.  The 
following  weights  are  given  : 


,  BaClr  ist  BaSO,.          2d  BaSO,. 

4.346  grm.  4.758  grm.  5.364  grm.  .115  grm. 

4-733     "  5.178    "  5-848    "  .147     " 

Hence  we  have  the  following  quantities  of  La,,(S04)3  proportional  to 
100  parts  of  BaS04.  Column  A  is  deduced  from  the  first  BaS04  and 
column  B  from  the  second,  after  the  manner  above  described  : 


A. 

B. 

81.022 
80.934 

83.281 
83.662 

Mean,  80.978,  ±  .030 
From  A 

Mean,  83.471,  - 
La 

b.I28 

n8  4.7 

From  B  .  . 

147.  n 

A  agrees  best  with  other  determinations,  although,  theoretically,  it  is 
not  so  good  as  B. 

Marignac's  second  method,  described  in  the  same  paper  with  the  forego- 
ing experiments,  consisted  in  mixing  solutions  of  La.,(S04\.5  with  solutions 
of  BaCl.2,  titrating  one  with  the  other  until  equilibrium  was  established. 
The  method  has  already  been  described  under  cerium.  The  weighings 

*  Poggend.  Annalen,  55,  65. 

t  Arch.  Sci.  Phys.  et  Nat.  (i),  n,  29.     1849. 


LANTHANUM. 


345 


give  maxima  and  minima  for  BaCl2.  In  another  column  I  give  La.,(S04)3 
proportional  to  100  parts  of  BaCl2,  mean  weights  being  taken  for  the 
latter : 

Ratio. 
91.004 
90.968 
91-297 
9'.332 
9r-362 

9L475 
91.364 
91.615 
91.482 

Mean,  91.322,  ±  .048 

Hence  La  =  140.2. 

Although  not  next  in  chronological  order,  some  still  more  recent  work 
of  Marignac's  *  may  properly  be  considered  here.  The  salt  studied  was 
the  sulphate  of  lanthanum,  purified  by  repeated  crystallizations.  In  two 
experiments  the  salt  was  calcined,  and  the  residual  oxide  weighed  ;  in 
two  others  the  lanthanum  was  precipitated  as  oxalate,  and  converted  into 
oxide  by  ignition.  The  following  percentages  are  given  for  La2O3 : 

"'5     I  By  calcination. 


La.,(SO 

BaClv 

1  1.  644  g 

m.           12.765  —  12.825 

12.035 

'              I3-i95  —  I3-265 

10.690 

'             11.669  —  11-749 

12.750 

13.920  —  14.000 

io.757 

11.734—  11.814 

12.672 

13-813  —  13.893 

9.246 

10.080  —  10.160 

10.292 

11.204  —  1  1.264 

10.192 

(             ii.  in  —  11.171 

57.58 
57.50 

57-55 


jPpt. 


as  oxalate. 


Mean,  57-5475,  ±  -OII5 

The  atomic  weight  determinations  of  Holzmann  f  were  made  by  analy- 
ses of  the  sulphate  and  iodate  of  lanthanum,  and  the  double  nitrate  of 
magnesium  and  lanthanum.  In  the  sulphate  experiments  the  lantha- 
num was  first  thrown  down  as  oxalate,  which,  on  ignition,  yielded  oxide. 
The  sulphuric  acid  was  precipitated  as  BaSO4  in  the  filtrate. 


•  5'57 
.3323 
.4626 


.9663  grm. 
.6226  " 
.8669  " 


1.1093  grm. 
.7123  " 
.9869  " 


These  results  are  best  used  by  taking  the  ratio  between  the  BaS04,  put 
at  100,  and  the  La,20.r     The  figures  are  then  as  follows  : 

46.489 
46652 
46.873 


Mean,  46.671,  ±  .075 


*  Ann.  Chim.  Phys.  (4),  30,  68.     1873. 
t  Journ.  fur  Prakt.  Chem.,  75,  321.     1858. 


346  THE    ATOMIC    WEIGHTS. 

In  the  analyses  of  the  iodate  the  lanthanum  was  thrown  down  as  oxa- 
late,  as  before.  The  iodic  acid  was  also  estimated  volumetrically,  but 
the  figures  are  hardly  available  for  present  discussion.  The  following 
percentages  of  La203  were  found  : 

23-454 
23.419 
23.468 

Mean,  23.447,  ±  .0216 

The  formula  of  this  salt  is  La2(I03)6.3H20. 

The  double  nitrate,  La2(N03)6.3Mg(N03)2.24H20,  gave  the  following 
analytical  data : 


Salt.         H^O.         MgO. 

•5327  grm-  •I569grm.  .0417  grm.  .1131  grm. 

•5931  "  -1734  "  -0467  "  .1262  " 

.S662  "  .1647  "  -0442  "  .1197  " 

•  3757  "         .0297  "  .0813  " 

.3263  <(         .0256  l<  .0693  " 

These  weighings  give  the  subjoined  percentages  of  La203 : 

21.231 

21.278 
21.141 

21.640 
21.238 


Mean,  21.3056,  ±  .058 

These  data  of  Holzmann  give  values  for  the  molecular  weight  of  La20s 
as  follows : 

From  sulphate , La2O3  =  322.460 

From  iodate "      —  320.726 

From  magnesian  nitrate "      =  322.904 

Czudnowicz*  based  his  determination  of  the  atomic  weight  of  lantha- 
num upon  one  analysis  of  the  air-dried  sulphate.  The  salt  contained 
22.741  per  cent,  of  water. 

.598  grm.  gave  .272  grm.  La2O3  and  .586  grm.  BaSO4. 

The  La203  was  found  by  precipitation  as  oxalate  and  ignition.  The 
BaSO4  was  thrown  down  from  the  filtrate.  Reduced  to  the  standards 
already  adopted,  these  data  give  for  the  percentage  of  La2O3  in  the  anhy- 
drous sulphate  the  figure  58.668.  79.117  parts  of  the  salt  are  propor- 
tional to  100  parts  of  BaSO4. 

*  Journ.  fur  Prakt.  Chem.,  So,  33.  1860. 


LANTHANUM.  347 

Hermann  *  studied  both  the  sulphate  and  the  carbonate  of  lanthanum. 
From  the  anhydrous  sulphate,  by  precipitation  as  oxalate  and  ignition, 
the  following  percentages  of  La2O3  were  obtained  : 


Mean,  57.654,  ±  .016 

The  carbonate,  dried  at  100°,  gave  the  following  percentages : 

68.47  La203. 

27.67  C02. 

3.86  H20. 

Reckoning  from  the  ratio  between  C02  and  La2O3,  the  molecular  weight 
of  the  latter  becomes  324.254. 

Zschiesche's  f  experiments  consist  of  six  analyses  of  lanthanum  sul- 
phate, which  salt  was  dehydrated  at  230°,  and  afterwards  calcined.  I 
subjoin  his  percentages,  and  in  a  fourth  column  deduce  from  them  the 
percentage  of  La203  in  the  anhydrous  salt : 

H^O.  SO3.  La-iO^     LazO3  in  Anhydrous  Salt. 

22.629  33-470  43.909  56.745 
22.562  33.306  44.132  56.964 
22.730  33.200  44.070  57-°34 
22.570  33-333  44.090  56.947 
22.610  33.160  44.24°  57-I5° 

22.630  33-051  44-310  57.277 

Mean,  57.021,  ±  .051 

Erk  J  found  that  .474  grm.  of  La2(S04)3,by  precipitation  as  oxalate  and 
ignition,  gave  .2705  grm.  of  La203,  or  57.068  per  cent.  .7045  grm.  of  the 
sulphate  also  gave  .8815  grm.  of  BaS04.  Hence  100  parts  of  BaS04  are 
equivalent  to  79.921  of  La2(S04)3. 

From  Cleve  we  have  two  separate  investigations  relative  to  the  atomic 
weight  of  lanthanum.  In  his  first  series  §  strongly  calcined  La203,  spec- 
troscopically  pure,  was  dissolved  in  nitric  acid,  and  then,  by  evaporation 
with  sulphuric  acid,  converted  into  sulphate : 

1.9215  grm.  La2O3  gave  3.3365  grm.  sulphate.  57-59°  Per  cent. 


2.0570 

3.5705 

57.6ii 

it 

1.6980             " 

2.9445 

57.667 

<  < 

2.0840               " 

3.6170 

57.6i7 

« 

1.9565     ,     " 

3.396o 

57.612 

11 

Mean,  57.619, 

rb  .0085 

*  Journ.  fur  Prakt.  Chem.,  82,  396.     1861. 

t  Journ.  fur  Prakt.  Chem.,  104,  174. 

I  Jenaisches  Zeitschrift,  6,  306.     1871. 

g  K.  Svensk.  Vet.  Akad.  Handlingar,  Bd.  2,  No.  7.     1874. 


348  THE    ATOMIC    WEIGHTS. 

From  the  last  column,  which  indicates  the  percentage  of  La2O3  in 
La2(S04)3,  we  get,  if  SO,  =*  80,  La  =  139.15. 

In  his  second  paper,*  published  nine  years  later,  Cleve  gives  results 
similarly  obtained,  but  with  lanthanum  oxide  much  more  completely 
freed  from  other  earths.  The  data  are  as  follows,  lettered  to  correspond 
to  different  fractions  of  the  material  studied : 

B-        '839°  Srm.  La2O3  gave  1.4600  sulphate.        57.466  per  cent. 

fi.i86i  2.0643  "  57458  " 

c    I     -8993  "               L5645  "  57.482  « 

'    |     .8685  1.5108  "  57.486  " 

I    .8515  "               1.4817  "  57.468  " 

D    I    .6486  "               1.1282  "  57.490  " 

'  1    .7329  1.2746  «  57oOO  " 

E.      1.2477  2.1703  "  57.490 

F   |  1.1621  2.0217  "  57.481 

'  i  1-5749  "              2.7407  "  57-463  " 

G   |  1.3367  2.3248  "  57.497  " 

.4455  "              2.5146  "  57-484  " 


Mean,  57.480,  dz  .0040 

Hence  with  S03  =  80,  La  =  138.22. 

From  Brauner  we  also  have  two  sets  of  determinations,  both  based  upon 
the  conversion  of  pure  La2O3  into  La2(S04)3. 

In  his  first  paper,  Brauner  f  gives  only  two  syntheses,  as  follows: 

1-75933  grm-  La2O3  gave  3.05707  Laa(SO4)3.  57-566  per  cent. 

.92417  "  1.60589         "  57-549 

Mean,  57-5575 

This  mean  we  may  regard  as  of  equal  weight  with  Marignac's,  and 
assign  to  it  the  same  probable  error. 

In  Brauner's  second  paper  J  six  experiments  are  given ;  but  the  weights 
are  affected  by  a  misprint  in  the  second  determination,  which  I  am  un- 
able to  correct.  Only  five  of  the  syntheses,  therefore,  are  given  below. 

•7850  grm.  La2O3  gave  1.3658  La2(SO4)3.  57-476  per  cent. 

2.1052  "  3-6633         "  57.467       " 

i. ooio  "  I-74H          "  57-525 

1.3807  "  2.4021         "  57-479       " 

1.5275  "  2.6588         "  57.451 


Mean,  57.480,  db  .0084 

Brauner's  weighings  are  all  reduced  to  a  vacuum. 

Both  Bauer  and  Bettendorff  made  their  determinations  of  the  atomic 

*  K.  Sveiisk.  Vet.  Akad.  Handlingar,  No.  2,  1883. 

t  Journ.  Chem.  Soc.,  Feb.,  1882,  p.  68. 

I  Sitzuugsb.  Wien.  Akad.,  June,  18*2,  Bd.  86,  II  Abth. 


LANTHANUM.  349 

weight  of  lanthanum  by  the  same  general  method  as  the  preceding 
Bauer's  data  *  are  as  follows  : 

.6431  grm.  La2O3  gave  1.1171  sulphate.  57.569  per  cent. 

.7825  "  1.3613         "  57.482       " 

1.0112  "  I.757I         "  57-549       " 

.7325  "  1.2725         "  57.564       " 

Mean,  57.541,  =b  .0136 

Bettendorff  found  f- 

.9146  grm.  La2O3  gave  1.5900  sulphate.  57-522  per  cent. 

-9395  "  '.6332         "  57.525       " 

.9133  "  I-5877         "  57.523       " 

1.0651  1.8515         "  57.526       " 

Mean,  57.524,  ±  .0006 

We  may  now  combine  the  similar  means  into  general  means,  and  de- 
duce a  value  for  the  atomic  weight  of  lanthanum.  For  the  percentage  of 
oxide  in  sulphate  we  have  estimates  as  follows.  The  single  experiments 
of  Czudnowicz  and  of  Erk  are  assigned  the  probable  error  and  weight  of 
a  single  experiment  in  Hermann's  series : 

Czudnowicz 58.668,    =b  .027 

Erk 57.o68,    ±  .027 

Hermann 57-654,    rfc  .016 

Zschiesche 57-O2I,    ±.051 

Marignac 57-5475,  ±  .01 15 

Cleve,  earlier  series 57-6i9,    ±  .0085 

Cleve,  later  series 57-48o,    ±  .0040 

Brauner,  earlier  series 57-5575,  =b  -OI !5 

Brauner,  later  series 57.480,    ±  .0084 

Bauer 57-541,    db  .0136 

Bettendorff. 57-524,    ±  .0006 


General  mean 57.522,    ±  .00059 

This  result  is  practically  identical  with  that  of  Bettendorff,  whose  work 
seems  to  receive  excessive  weight.  The  figure,  however,  cannot  be  far 
out  of  the  way. 

For  the  quantity  of  La2(S04)3  proportional  to  100  parts  of  BaSO4.  we 
have  five  experiments,  which  may  be  given  equal  weight  and  averaged 
together : 

Marignac , 81.022 

Marignac 80.934 

Rammelsberg 79.276 

Czudnowicz 79. 1 1 7 

Erk 79.921 

Mean,  80.054,  ±  .270 

*  Freiburg  Inaugural  Dissertation,  1884. 
i  Ann.  d.  Chem.,  256,  168. 


350  THE    ATOMIC    WEIGHTS. 

Iii  all,  there  are  six  ratios  from  which  to  calculate : 

(i.)  Percentage  of  La.2O3  in  La2(SO4)3,  57.522,  ±  .00059 

(2.)  3BaCl.2  :  La2(SO4)3  :  :  ioo  :  91.322,  ±  .048— Marignac 

(3.)  3BaSO4  :  La2(SO4)3  :  :  ioo  :  80.054,  ±  .270 

(4.)  3BaSO4  :  La2O3  :  :  ioo  :  46.671,  ±  .075— Holzmann 

(5.)  Percentage  of  La2O3  in  iodate,  23.447,  dr  .0216 — Holzmann 

(6.)  Percentage  of  La2O3  in  magnesian  nitrate,  21.3056,  ±  .058 — Holzmann 

Hermann's  single  experiment  on  the  carbonate  is  omitted  from  this 
scheme  as  being  unimportant. 

For  the  reduction  of  these  data  we  have — 

O=     15.879,  zh. 0003  N     ::     13.935,  ±  .0021 

Cl  —  35.179,  ±  .0048          C  =  11.920,  ±  .0004 
I  =  125.888,  ±  .0069  Mg  =  24.  ioo,  =b  .001 1 

S  =  31.828,  ±  -0015  Ba  ==  136.392,  ±  .0086 

For  lanthanum  sulphate  two  values  are  obtainable  : 

From  (2) La2(SO4)3  =  566.425,  ±    .2999 

From  (3) "         =  556.542,^1.8729 


General  mean Ln2(SO4)3  =  566. 182,  rh    .2961 

Hence  La  =  140.075,  ±  .1481. 

For  the  oxide  there  are  four  independent  values,  as  follows : 

From  (i) La2O3  =  322.825,  ±  .0090 

From  (4) "      =  322.460,^.5215 

From  (5) "      =320.726,^.3159 

From  (6) "       =  322.904,  ±  .9107 

A  glance  at  these  figures  shows  that  the  first  alone  deserves  considera- 
tion, and  that  a  combination  of  all  would  vary  inappreciably  from  it. 
Taking,  then,  La203  =  322.825,  =fc  .0090,  we  get- 
La  =  137.594,  =b  .0046; 

or,  with  0  =  16,  La  =  138.642. 

If  we  take  the  concordant  results  of  Cleve's  and  Brauner's  later  series, 
which  give  the  percentage  of  La203  in  La2(S04)3  as  57.480,  then  La  = 
137.316.  Possibly  this  value  may  be  better  than  the  other,  but  the  evi- 
dence is  not  conclusive. 


THE    DIDYMIUMS.  351 


THE  DIDYMIUMS. 

Leaving  Mosander's  early  experiments  out  of  account,  the  atomic 
weight  of  the  so-called  u  didymium  "  was  determined  by  Marignac,  Her- 
mann, Zschiesche,  Erk,  Cleve,  Brauner,  and  Bauer.  All  of  these  data 
now  have  only  historical  value,  and  may  be  disposed  of  very  briefly. 

Marignac*  determined  the  ratios  between  didymium  sulphate  and 
barium  sulphate,  between  silver  chloride  and  didymia,  and  between 
didymium  sulphate  and  didymium  oxide.  The  other  determinations  all 
relate  to  the  sulphate-oxide  ratio.  Leaving  all  else  out  of  account,  the 
earlier  data  for  the  percentage  of  Di2O3  in  Di2(SO4)3  are  as  follows.  The 
atomic  weight  of  Di  in  the  last  column  is  based  upon  SO3  =  80  : 

Per  cent.  Z?/2Oj.      At.  Wt.  Di. 

Marignac,  f  five  experiments 58.270  !43-56 

Hermann,  J  one  experiment 58.140  142.67 

Zschiesche,^  five  experiments  ....    57-926  141.21 

Erk,  ||  two  experiments 58.090  i42-33 

Cleve, ^[  six  experiments 58.766  147.02 

Brauner,**  three  experiments 58.681  146.42 

The  discordance  of  the  determinations  is  manifest,  and  yet  up  to  1883 
the  elementary  nature  of  didymium  seems  to  have  been  undoubted.  In 
that  year,  however,  Cleve  and  Brauner  both  showed,  independently,  that 
the  didymia  previously  studied  by  them  contained  samaria,  and  that 
source  of  disturbance  was  eliminated. 

In  Brauner 's  investigation  ft  the  didymium  compounds  were  carefully 
fractionated,  and  the  determinations  of  atomic  weight  were  made  by 
synthesis  of  the  sulphate  from  the  oxide  in  the  usual  way.  Neglecting 
details,  his  first  series  gave  results  as  follows : 

Per  cent.  Di^Oy  At.  Wt. 

58-5°6  I45-36 

58-526  145.50 

58.5°°  145-31 

58-515  I45-42 

58.531  145-53 

*Two  papers:  Arch.  Sci.  Phys.  et  Nat.  (i),  n,  29.     1849.     Ann.  Chim.  Phys.  (3),  38,  148.     1853. 
f  Ann.  Chim.  Phys.  (3),  38,  148.     1853. 
|  Journ.  fur  Prakt.  Chem.,  82,  367.     1861. 
\  Journ.  fi'ir  Prakt.  Chem.,  107,  74. 
||  Jenaisches  Zeitschrift,  6,  306.     1871. 
f  K.  Svensk.  Vet.  Akad.  Handl.,  Bd.  2,  No.  8.     1874. 
**  Berichte,  15,  109.     1882. 

ft  Journ.  Chem.  Soc.,  June,  1883.  The  values  given  are  as  computed  by  Brauner,  with  O  =  16 
and  S  =  32.07. 


352  THE    ATOMIC    WEIGHTS. 

Another  determination,  with  material  refractionated  from  that  used  in 
his  investigation  of  the  previous  year,  gave  58.512  per  cent.  Di.203  and 
Di  =  145.40. 

These  determinations,  although  concordant  among  themselves,  are 
still  about  a  unit  lower  than  those  published  in  1882,  indicating  that  in 
the  earlier  research  some  earth  of  higher  molecular  weight  was  present. 
Accordingly,  another  series  of  fractionations  was  carried  out,  and  the 
several  fractions  of  "  didyrnia  "  obtained  gave  the  following  values  : 
Fraction.  Per  cent.  Di^O^.  At.Wt.^Di." 

i 58.355  H4.32 

2 58.479  i45-16 

3 58-5»o  145-39 

4 58.755  i47.io 

c  J  59.071  149.35 

' '  1  59-086  149.46 

The  last  fraction  is  evidently  near  samaria  (Sm  =  150),  and  this  earth 
was  proved  to  be  present  by  a  study  of  the  absorption  spectra  of  the 
material  investigated. 

Similar  results,  but  in  some  respects  more  explicit,  were  obtained  by 
Cleve,*  who  also  found  that  his  earlier  research  had  been  vitiated  by  the 
presence  of  samaria.  He  gives  two  series  of  syntheses  of  sulphate  from 
oxide,  with  two  different  lots  of  material,  after  eliminating  samaria,  and 
obtains,  computing  with  S03  =  80,  values  for  Di  as  follows  : ' 

First  Series. 

Per  cent.  Di2O3.  At.  Wt.  Di. 

58.088  142.31 

58.113  142.49 

58.047  142-03 

58.099  142.39 

58.104  142.42 

58.098  142.38 

58.104  142.42 

58.103  142.42 

58.070  142.19 

58.079  142.25 

Second  Series. 

Percent.  £>/26>3.  At.  Wt.  Di. 

58.125  142.57 

58-093  H2.35 

58.088  142.31 

58.111  142.47 

58.056  142.10 
58.097  142.38 

58.057  142.10 

In  short,  the  atomic  weight  of  this  "  didymium  "  is  not  far  from  142. 

*Bull.  Soc.  Chim.,  39,  289.     1883.     Ofv.  K.  Vet.  Akad.  Forhandl.,  No.  2,  1883. 


THE    DIDYMIUMS.  353 

Bauer's  little  known  determinations*  were  also  made  by  the  synthesis 
of  the  sulphate.  They  have  corroborative  value  and  are  as  follows  : 

Per  cent.  £>/2<93.  At.  Wt.  Di. 

58.285  I43-56 

58.100  142.40 

58.133  142.64 

58.098  142.38 

In  1885  all  of  the  foregoing  determinations  were  practically  brushed 
aside  by  Auer  von  Welsbaeh,f  who  by  the  most  laborious  fraction ations 
proved  that  the  so-called  "  didymia  "  was  really  a  mixture  of  oxides, 
whose  metals  he  names  neodidymium  and  praseodidymium,  names 
which  are  now  commonly  shortened  into  neodymium  and  praseodymium. 
One  of  these  metals  gives  deep  rose-colored  salts,  the  other  forms  green 
compounds,  and  the  difference  of  color  is  almost  as  strongly  marked  as 
in  the  cases  of  cobalt  and  nickel.  Their  atomic  weights,  determined  by 
the  sulphate  method,  are  given  by  Welsbach  a  — 

Pr  =  143.6 
Nd  =  140.8 

No  further  details  as  to  these  determinations  are  cited,  and  whether 
they  rest  upon  0  =  16,  S03  =  80,  or  0  =  15.96  is  uncertain.  Fuller  deter- 
minations are  evidently  needed. 

*  Freiburg  Inaugural  Dissertation,  1884.. 
t  Monatsh.  Chem.,  6.  4QO.     1885. 


23 


354  THE    ATOMIC    WEIGHTS. 


SCANDIUM. 

Clove,*  who  was  the  first  to  make  accurate  experiments  on  the  atomic 
weight  of  this  metal,  obtained  the  following  data  :  1.451  grm.  of  sulphate, 
ignited,  gave  .5293  grm.  of  Sc203.  .4479  grin,  of  Sc203,  converted  into 
sulphate,  yielded  1.2255  grm.  of  the  latter,  which,  upon  ignition,  gave 
.4479  grin,  of  Sc203.  Hence,  for  the  percentage  of  £c203  in  Sc2(S04)s  we 
have : 

36.478 

36.556 

36.556 

Mean,  36.530,  ±  .0175 

Hence,  if  SO,  =  79.465,  Sc  =  44.882. 

Later  results  are  those  of  Nilson,t  who  converted  scandium  oxide  into 
the  sulphate.  I  give  in  a  third  column  the  percentage  of  oxide  in  sul- 
phate : 

.3379  grm.  Sc203  gave  .9343  grm.  Sc2(SO4)3.  36.166  per  cent. 

.3015  .8330  36.194 

.2998  "  .8257  "  36.187        " 

.3192  "  •    .8823  "  36-178        " 


Mean,  36.181,  db  .004 

Hence  Sc  ==  43.758. 

Combining  the. two  series,  we  have — 

Cleve 36.530,  =b  .0175 

Nilson    36. 1 8 1 ,  ±  .0040 


General  mean 36. 190,  ±  .0039 

Hence,  with  SO,  =  79.465,  ±  .00175, 

Sc  =  43.784,  ±  .0085. 

If  0  =  16,  Sc  — 44.118. 

As  between  the  two  values  found,  the  presumption  is  in  favor  of  the 
lower.  The  most  obvious  source  of  error  would  be  the  presence  in  the 
scandia  of  earths  of  higher  molecular  weight. 

*Compt.  Rend.,  89,  419. 
fCompt.  Rend.,  91,  118. 


YTTRIUM.  355 


YTTRIUM. 

All  the  regular  determinations  of  the  atomic  weight  of  yttrium  depend 
upon  analyses  or  syntheses  of  the  sulphate.  A  series  of  analyses  of  the 
oxalate,  however,  by  Berlin,*  is  sometimes  cited,  and  the  data  are  as  fol- 
lows. In  three  experiments  upon  the  salt  Yt/C204)3  3H,0  the  subjoined 
percentages  of  oxide  were  found  : 

45-70 
45-^5 
45-72 


Mean,  45.69,  dz  .0141 

Hence  with  0  =  15.879  and  C  =  11.920, 


Yt  ==  88.943. 

Ignoring  the  early  work  of  Berzelius,f  the  determinations  to  be  con- 
sidered are  those  of  Popp,  Delafontaine,  Bahr  and  Bunsen,  Cleve,  and 
Jones. 

Popp  t  evidently  worked  with  material  not  wholly  free  from  earths  of 
higher  molecular  weight  than  yttria.  The  yttrium  sulphate  was  dehy- 
drated at  200°  ;  the  sulphuric  acid  was  then  estimated  as  barium  sul- 
phate, and  after  the  excess  of  barium  in  the  filtrate  had  been  removed 
the  yttrium  was  thrown  down  as  oxalate  and  ignited  to  yield  oxide- 
The  following  are  the  weights  given  by  Popp : 

Sulphate.  BaSO±.  Y^O3.  H.2O. 

1.1805  grm.  *-3l45  grm-  -4742  grni.  .255  grm. 

1.4295     «  1.593       "  -5745     "  -308    " 

.8455    "  .9407     "  .3392    "  .1825  " 

1.045      "  1.1635     "  .4195    "  .2258  " 

Eliminating  water,  these  figures  give  us  for  the  percentages  of  Yt203  in 
Yt2(SOj3  the  values  in  column  A.  In  column  B  I  put  the  quantities  of 
Yt203  proportional  to  100  parts  of  BaS04 : 

A.  B. 

51.237  36.075 

51.226  36.064 

51.161  36.058 

51-209  36.055 

Mean,  51.208,  ±  .on  Mean,  36.063,  ±  .003 

From  B,  Yt  =  101.54.  The  values  in  A  will  Be  combined  with  similar 
data  from  other  experimenters. 

*  Forhandlingar  ved  de  Skaiidinaviske  Naturforskeres,  8,  452.     1860. 

f  lyehrbuch,  V  Aufl.,  3,  1225. 

I  Ann.  Chem.  Pharm.,  131,  179.     1804. 


356  THE    ATOMIC    WEIGHTS. 

In  1865  Delafontaine*  published  some  results  obtained  from  yttrium 
sulphate,  the  yttrium  being  thrown  down  as  oxalate  and  weighed  as 
oxide.  In  the  fourth  column  I  give  the  percentages  of  Yt203  reckoned 
from  the  anhydrous  sulphate : 


Sulphate. 

Yt2  <93. 

H.jp. 

Percent.  ] 

•9545  Srm- 

.371  grm. 

.216  grm. 

50.237 

2.485      " 

.9585   " 

.565      " 

49.922 

2.153      " 

.827      » 

•4935  " 

49.834 

Mean,  49.998,  =b  .081 

In  another  paper  f  Delafontaine  gives  the  following  percentages  of 
Yt.203  in  dry  sulphate.  The  mode  of  estimation  was  the  same  as  before  : 

48.23 
48.09 
48-37 

Mean,  48.23,  ±  .055 

Bahr  and  Bunsen,  J  and  likewise  Cleve,  adopted  the  method  of  con- 
verting dry  yttrium  oxide  into  anhydrous  sulphate,  and  noting  the  gain 
in  weight.  Bahr  and  Bunsen  give  us  the  two  following  results.  I  add 
the  usual  percentage  column  : 

Yt.203.  Yt^SO^  Percent.  F/26>3. 

.7266  grm.  L4737  grm.  49.3°4 

.7856     "  L5956     "  49-235 

Mean,  49.2695,  ±  .0233 

Cleve's  first  results  are  published  in  a  joint  memoir  by  Cleve  and 
Hoeglund,§  and  are  as  follows  : 


Percent. 

1.  4060  grm.  2.  8925  grm.  48.608 

1.0930    "  2.2515     "  48.545 

1.4540     "  2.9895     "  48.637 

1.3285     "  2.7320     "  48.627 

2.3500    "  4-833°    "  48.624 

2.5780    "  5.3055     "  48.591 


Mean,  48.605,  =h  .0096 

In  a  later  paper  Cleve  ||  gives  syntheses  of  yttrium  sulphate  made  with 
yttria,  which  was  carefully  freed  from  terbia.  The  weights  and  percent- 
ages are  as  follows : 

*Ann.  Chem.  Pharm.,  134,  108.     1865. 

t  Arch.  Sci.  Phys.  et  Nat.  (2),  25,  119.     1866. 

J  Ann.  Chem.  Pharm.,  137,  21.     1866. 

g  K.  Svenska  Vet.  Akad.  Handlingar,  Bd.  i,  No.  S.    1873. 

|j  K.  Svenska  Vet.  Akad.  Handlingar,  No.  9,  1882.     See  also  Bull.  Soc.  Chim.,  39,  120.     1883. 


YTTRIUM.  357 

yt.2O3.  y/2(S04)3.  Percent.  Yt.tOz. 

.8786  1.8113  48/507 

.8363  .7234  48.526 

.8906  .8364  48.497 

.7102  .4645  48.494 

.7372  .5194  48.519 

.9724  .0047  48.506 

.9308  .9197  48.487 

.8341  .7204  48.483 

1.0224  2.1073  48.5*7 

.9384  i.934i  48.519 

•  9744  2.0093  48.494 

1.53*4  3.1586  48.484 

Mean,  48.503,  ±  .0029 

Hence  Yt  =  88.449. 

The  y  ttria  studied  by  Jones*  had  been  purified  by  Rowland's  method- 
thai  is,  by  precipitation  with  potassium  ferrocyanide— and  certainly  con- 
tained less  than  one-half  of  one  per  cent,  of  other  rare  earths  as  possible 
impurities.  Two  series  of  determinations  were  made — one  by  ignition  of 
the  sulphate,  the  other  by  its  synthesis.  The  results  were  as  follows,  with 
the  usual  percentage  column  added : 

First  Series.     Syntheses. 


Yt^Oy 

Yt^SO^. 

Percent.  Yt2Os. 

.2415 

.4984 

48.455 

.41  12 

.8485 

48.462 

.2238 

.4617 

48.473 

•3334 

.6879 

48.466 

.3408 

.7033 

48.457 

.3418 

.7049 

48.489 

.2810 

.5798 

48.465 

.3781 

.7803 

48.456 

•4379 

.9032 

48.483 

.4798 

.9901 

48.460 

Mean,  48.467,  ±  .0025 

Second  Series.  Analyst. 

58. 

Ytz(SO4)3. 

Yt,0,. 

Percent.  Yt.2O3. 

.5906 

.2862 

48.459 

.4918 

.2383 

48.455 

.5579 

.2705 

48.485 

.6430 

.3"7 

48.478 

.6953 

.3369 

48.454 

1.4192 

.6880 

48.478 

.8307 

.4027 

48.477 

.7980 

.3869 

48.484 

.8538 

.4*39 

48.477 

1.1890 

.5763 

48.469 

Mean,  48.472,  ±  .0024 

*  Anier.  Chem.  Journ.,  17,  154.     1895. 


358  THE    ATOMIC    WEIGHTS, 

From  syntheses Yt  =  88. 287 

From  analyses "  =  88.309 

These  data  of  Jones  were  briefly  criticised  by  Delafontaine,*  who  re- 
gards a  lower  value  as  more  probable.  In  a  brief  rejoinder  f  Jones 
defended  his  own  work;  but  neither  the  attack  nor  the  reply  needs 
farther  consideration  here.  They  are  referred  to  merely  as  part  of  the 
record. 

For  the  percentage  of  yttria  in  the  sulphate  we  now  have  eight  series 
of  determinations,  to  be  combined  in  the  usual  way  : 

Popp 51.208,  rb  .01 10 

Delafontaine,  first 49,998,  rb  .0810 

Delafontaine,  second 48.230,  ±  .0550 

Bahr  and  Bunsen 49.2695,  rb  .0233 

Cleve,  earlier 48.605,  db  .0096 

Cleve,  later 48.503,  ±  .0029 

Jones,  syntheses 48.467,  rb  .0025 

Jones,  analyses 48.472,  rb  .0024 


General  mean 48.532,    rb  .0015 

Hence,  if  0  =  15.879,  ±  .0003,  and  S  =  31.828,  ±  .0015, 

Yt  =  88.580,  rb  .0053. 

If  0  =  16,  Yt  =  89.255. 

If  only  the  four  series  by  Cleve  and  by  Jones  are  considered,  the  mean 
percentage  of  yttria  in  the  sulphate  becomes  48.481.  Hence  Yt  =  88.350, 
or,  with  0  =  16,  89.023. 

This  result  is  preferable  to  that  derived  from  all  the  data,  for  it  throws 
out  determinations  which  are  certainly  erroneous.  Cleve's  early  series 
might  also  be  rejected,  but  its  influence  is  insignificant. 

*Chem.  News,  71,  243. 
fChem.  News,  71,  305. 


SAMARIUM,    GADOLINIUM.    ETC. 


SAMARIUM,  GADOLINIUM,  ERBIUM,  AND  YTTERBIUM. 

The  data  relative  to  the  atomic  weights  of  these  rare  elements  are 
rather  scanty,  and  all  depend  upon  analyses  or  syntheses  of  the  sul- 
phates. 

SAMARIUM. 

Atomic  weight  given  by  Marignac,*  without  details,  as  149.4,  and  by 
Brauner,f  as  150.7  in  maximum.  The  first  regular  series  of  determina- 
tions was  by  Cleve,  J  who  effected  the  synthesis  of  the  sulphate  from  the 
oxide.  Data  as  follows  : 


Sm2O3.  Sm.i(SOJ3.  Per  cent. 

1.6735  2.8278  59-l8° 

i.97o6  3.3301  59-  '75 

I.II22  1.8787  59-201 

1.0634  1.7966  S9-19° 

.8547  1.4440  59.J90 

•7447  1-2583  59-183 


Mean,  59.1865,  ±  .0025 

Hence  Sm  =  149.038. 

Another  set  of  determinations  by  Bettendorff,§  after  the  same  general 
method,  gave  as  follows: 

Sm.,O.A.  Sm^SO^.  Per  cent.  Sm.2O3. 
1.0467                                1.7675  59-219 

1.0555  1.7818  59.238 

1.0195  1.7210  59.225 

Mean,  59,227,  ±  .0038 

Hence  Sm  =  149.328.  v 

Combining  the  two  series,  we  have  — 

Cleve  ..................................    59.  1865,  =  .0025 

Bettendorff  .............................    59.227,    ±  .0038 


General  mean 59.1 99,    =h  .002  r 

Hence,  if  S03  =  79.465,  ±  .00175, 

Sm  =  149. 127,  =b  .01 15. 

If  0=16,  Sm  =  150.263*. 

According  to  Demarcay.||  samaria  contains  an  admixed  earth  whose 
properties  are  yet  to  be  described. 

*  Arch.  Sci.  Phys.  et  Nat.  (3),  3,  435.     1880. 

t  Journ.  Chem.  Soc.,  June,  1883. 

1  Journ.  Chem.  Soc.,  August,  1883.     Conipt.  Rend.,  97,  94. 

gAnn.  Chem.  Pharm.,  263,  164.     1891. 

j|  Compt.  Rend.,  122,  728.     1896. 


360  THE    ATOMIC    WEIGHTS. 

GADOLINIUM. 

This  element,  discovered  by  Marignac,  must  not  be  confounded  with 
the  mixture  of  metals  from  the  gadolinite  earths  to  which  Nordenskiold 
gave  the  same  name.  Several  determinations  of  its  atomic  weight  have 
been  made,  but  Bettendorff's  only  were  published  with  proper  details.* 
He  effected  the  synthesis  of  the  sulphate  from  the  oxide,  and  his  weights 
were  as  follows.  The  percentage  of  Gd2O8  in  Gd2(SOJ3  is  given  in  the 
third  column : 


Gd.2O.A.  Gd^SO^.  Percent.  G 

1.0682                               1-7779  60.082 

1.0580                               1.7611  60.076 

1.0796                               1.7969  60.081 


Mean,  60.080,  ±  .0013 

Hence,  with  S03  =  79.465,  Gd  =  155.575. 
If  0  =  16,  Gd«  156.761, 

Boisbaudranf  found  Gd  =  155.33, 156.06, 155.76,  and  156.12.  The  last 
he  considers  the  best,  but  gives  no  details  as  to  antecedent  values.  He 
also  quotes  Marignac,  who  found  Gd  —  156.75,  and  Cleve,  who  found 
154.15,  155.28,  155.1,  and  154..77.  Probably  these  all  depend  upon 

S03  =  80. 

ERBIUM. 

Since  the  earth  which  was  formerly  regarded  as  the  oxide  of  this  metal 
is  now  known  to  be~a  mixture  of  two  or  three  different  oxides,  the  older 
determinations  of  its  molecular  weight  have  little  more  than  historical 
interest.  Nevertheless  the  work  done  by  several  investigators  may  prop- 
erly be  cited,  since  it  sheds  some  light  upon  certain  important  problems. 

First,  Delafontaine's  J  early  investigations  may  be  considered.  A  sul- 
phate, regarded  as  erbium  sulphate,  gave  the  following  data.  An  oxalate 
was  thrown  down  from  it,  which,  upon  ignition,  gave  oxide.  The  per- 
centages in  the  fourth  column  refer  to  the  anhydrous  sulphate.  In  the 
last  experiment  water  was  not  estimated,  and  I  assume  for  its  water  the 
mean  percentage  of  the  four  preceding  experiments  : 

Sulphate.  £r2O3.  ff.2O.  Per  cent.  ErzO3. 

.827  grm.  .353  grm.  .177  grm.  54. 308 

1.0485  "  .4475  "  .226  "  54.407 

.803  "  .3415  "  .171^  "  54.035 

1.232  "  .523  "  .264"  "  54.028 

1.1505  "  .495  "  54-76o 


Mean,  54.308,  zb  .0915 

Hence  Er  =  117.86. 

*  Ann.  Chem.  Pharm.,  270,  376.     1892. 

t  Compt.  Rend.,  in,  409.     1890. 

J  Ann.  Chem.  Pharm.,  134,  108.     1865. 


ERBIUM,    YTTERBIUM,    ETC.  361 

Bahr  and  Bunsen  *  give  a  series  of  results,  representing  successive  puri- 
fications of  the  earth  which  was  studied.  The  final  result,  obtained  by 
the  conversion  of  oxide  into  sulphate,  was  as  follows : 

.7870  grm.  oxide  gave  1.2765  grm.  sulphate.     61.653  Per  cent,  oxide. 

Hence  Er  =  167.82. 

Hoeglund,  f  following  the  method  of  Bahr  and  Bunsen,  gives  these 

results  : 

Er.2O,.  Er^(SO^.A.  Per  cent.  Er.2O3. 

1 .8760  grm.  3.0360  grm.  61.792 

1.7990     "  2.9100     "  61.821 

2.8410     "  4-5935     "  61.848 

1.2850     "  2.0775     "  61.853 

1.1300     "  1.827       "  61.850 

.8475    "  r-37Q      "  61.861 

'  Mean,  61.8375,  ±  .0063 
Hence  Er  =  169.33. 

According  to  Thalen,t  spectroscopic  evidence  shows  that  the  "  erbia  " 
studied  by  Hoeglund  \vas  largely  ytterbia. 
Humpidge  and  Burney  §  give  data  as  follows : 

1.9596  grm.  Er2(SO4)3  gave  1.2147  grm-  Er.2O3.       61.987  per  cent. 
1.9011  "  1.1781          "  61.965         " 

Mean,  61.976,  ±  -0074 

Hence  Er=  170.46. 

The  foregoing  data  were  all  published  before  the  composite  nature  of 
the  supposed  erbia  was  fully  recognized.  It  will  be  seen,  however,  that 
three  sets  of  results  were  fairly  comparable,  while  Delafontaine  evidently 
studied  an  earth  widely  different  from  that  investigated  by  the  others. 
Since  the  discovery  of  ytterbium,  some  light  has  been  thrown  on  the 
matter.  The  old  erbia  is  a  mixture  of  several  earths,  to  one  of  which,  a 
rose-colored  body,  the  name  erbia  is  now  restricted.  For  the  atomic 
weight  of  the  true  erbium  Cleve  ||  gives  three  determinations,  based  on 
syntheses  of  the  sulphate  after  the  usual  method.  His  weights  were  as 
follows,  with  the  percentage  ratio  added  : 

Er.2O3.  Er.i(SO^y  Per  cent.  Er.2O3. 
1.0692                                1.7436  61.321 

1.2153  1.9820  61.317 

.7850  1.2808  61.290 

Mean,  61.309,  d=  .0068 

Hence,  with  S03  =  79.465,  Er  ==  165.059. 
If  0  =16,  Er=  166.316. 

*Ann.  Chem.  Pharm.,  137,  21.     1866. 

fK.  SvenskaVet.  Akad.  Handlingar,  Bd.  i,  No.  6. 

I  Wiedemann's  Beibliitter,  5,  122.     1881. 

#  Journ.  Chem.  Soc.,  Feb.,  1879,  p.  116. 

||  K.  Svensk.  Vet.  Akad.  Handlingar,  No.  7,  1880.     Abstract  in  Compt.  Rend.,  91,  382. 


362  THE    ATOMIC    WEIGHTS. 

It  is  not  worth  while  to  combine  this  result  with  the  earlier  determi- 
nations, for  they  are  now  worthless. 


YTTERBIUM. 


For  ytterbium  we  have  one  very  good  set  of  determinations  by  Nilson.* 
The  oxide  was  converted  into  the  sulphate  after  the  usual  manner : 


1.0063  grm- 

1.0139  " 

.8509  " 

.7371  " 

1.0005  " 

.8090  " 

1.0059  " 


Percent.  Y&.2O3. 

.6186  giro.  62.171 

.6314     "  62.149 

.3690    "  62.155 

.1861     "  62.145 

.6099     "  62.147 

.3022     "  62.126 

.6189     <(  62.134 


Mean,  62.147,  ±  .0036 


Hence,  with  S03  =  79.465,  Yb  =  171.880. 
If  O  =  16,  Yb  =  173.190. 


TERBIUM,  THULIUM,  HOLMIUM,  DYSPROSIUM,  ETC. 

For  these  elements  the  data  are  both  scanty  and  vague.  Concerning 
the  atomic  weights  of  holmium  and  dysprosium,  practically  nothing  has 
been  determined.  To  thulium,  Clevef  assigns  a  value  of  Tm  =  170.7, 
approximately,  but  with  no  details  as  to  weighings.  Probably  the  value 
was  computed  with  S03  =  80. 

For  terbium,  ignoring  older  determinations,  Lecoq  de  Boisbaudran  has 
published  two  separate  estimates.]!  First,  for  two  preparations,  one  with 
a  lighter  and  one  with  a  darker  earth,  he  gives  Tb  =  161.4  and  163.1 
respectively.  In  his  second  paper  he  gives  Tb  =  159.01  to  159.95.  These 
values  probably  are  all  referred  to  S03  =  80. 

*Compt.  Rend.,  91,  56.     1880.     Berichte,  13,  1430. 

t  Compt.  Rend.,  91,  329.     1880. 

J  Compt.  Rend.,  102,  396,  and  in,  474. 


ARGON    AND    HELIUM.  363 


ARGON  AND  HELIUM. 

The  true  atomic  weights  of  these  remarkable  gases  are  still  in  doubt, 
and  so  far  can  only  be  inferred  from  their  specific  gravities. 

For  argon,  the  discoverers,  Rayleigh  and  Ramsay,*  give  various  deter- 
minations of  density,  ranging,  with  hydrogen  taken  as  unity,  from  19.48 
to  20.6.  In  an  addendum  to  the  same  paper,  Ramsay  alone  gives  for 
the  density  of  argon  prepared  by  the  magnesium  method  the  mean  value 
of  19.941.  In  a  later  communication  f  Rayleigh  gives  determinations 
made  with  argon  prepared  by  the  oxygen  method,  and  puts  the  density 
at  19.940. 

For  the  density  of  helium,  Ramsay  J  gets  2.18,  while  Langlet§  finds 
the  somewhat  lower  value  2.00. 

From  one  set  of  physical  data  both  gases  appear  to  be  m  on  atomic,  but 
from  other  considerations  they  are  supposably  diatomic.  Upon  this 
question  controversy  has  been  most  active,  and  no  final  settlement  has 
yet  been  reached.  If  diatomic,  argon  and  helium  have'  approximately 
the  atomic  weights  two  and  twenty  respectively;  if  monatomic,  these 
values  must  be  doubled.  In  either  case  helium  is  an  element  lying  be- 
tween hydrogen  and  lithium,  but  argon  is  most  difficult  to  classify.  With 
the  atomic  weight  20,  argon  falls  in  the  eighth  column  of  the  periodic 
system  between  fluorine  and  sodium,  but  if  it  is  40  the  position  of  the  gas 
is  anomalous.  A  slightly  lower  value  would  place  it  between  chlorine 
and  potassium,  and  again  in  the  eighth  column  of  Mendelejeff's  table; 
but  for  the  number  40  no  opening  can  be  found. 

It  must  be  noted  that  neither  gas,  so  far,  has  been  proved  to  be  abso- 
lutely homogeneous,  and  it  is  quite  possible  that  both  may  contain  ad- 
mixtures of  other  things.  This  consideration  has  been  repeatedly  urged 
by  various  writers.  If  argon  is  monatomic,  a  small  impurity  of  greater 
density,  say  of  an  unknown  element  falling  between  bromine  and  rubid- 
ium, would  account  for  the  abnormality  of  its  atomic  weight,  and  tend 
towards  the  reduction  of  the  latter.  If  the  element  is  diatomic,  its  classi- 
fication is  easy  enough  on  the  basis  of  existing  data.  Its  resemblances 
to  nitrogen,  as  regards  density,  boiling  point,  difficulty  of  liquefaction, 
etc.,  lead  me  personally  to  favor  the  lower  figure  for  its  atomic  weight, 
and  the  same  considerations  may  apply  to  helium  also.  Until  further 
evidence  is  furnished,  therefore,  I  shall  assume  the  values  two  and  twenty 
as  approximately  true  for  the  atomic  weights  of  helium  and  argon. 

*  Phil.  Trans.,  186,  pp.  220  to  223,  and  238.     1,895. 

fChem.  News,  73,  75.     1896. 

JJourn.  Chem.  Soc.,  1895,  p.  684. 

\  Zeitsch.  Anorg.  Chem.,  10,  289.     1895. 


364 


THE    ATOMIC    WEIGHTS. 


TABLE  OF  ATOMIC  WEIGHTS. 

The  following  table  contains  the  values  for  the  various  atomic  weights 
found  or  adopted  in  the  preceding  calculations.  As  the  table  is  intended 
for  practical  use,  the  figures  are  given  only  to  the  second  decimal,  the 
third  being  rarely,  if  ever,  significant.  In  most  cases  even  the  first  deci- 
mal is  uncertain,  and  in  some  instances  whole  units  may  be  in  doubt. 

H  =  i.  0=16. 

Aluminum 26.91  27.11 

Antimony 119-S2  I2O43 

Argon ?  ? 

Arsenic 74-44  75-01 

Barium 136.39  r37-43 

Bismuth 206. 54  208. 1 1 

Boron 10.86  10.95 

Bromine 79-34  79-95 

Cadmiu'm ni.io  lll-95 

Caesium l3l-&9  132.89 

Calcium 39-76  40.07 

Carbon..., 11.92  12.01 

Cerium I39-IO  140.20 

Chlorine 35 .18  35-45 

Chromium 5!-74  52-J4 

Cobalt 58.49  58.93 

Columbium 93-Q2  93-73 

Copper 63. 12  63.60 

Erbium 165.06  166.32 

Fluorine 18.91  19.06 

Gadolinium , 155-57  156.76 

Gallium 69.38  69.91 

Germanium 7r-93  72.48 

Glucinum 9.01  9.08 

Gold 195-74  i97-23 

Helium ?  ? 

Hydrogen ....  i.ooo  1.008 

Indium 112.99  Ir3-^5 

Iodine 125.89  12685 

Iridium 191.66  '93-12 

Iron.. 55-6o  56.02 

Lanthanum T37-59  138.64 

Lead , 205.36  206.92 

Lithium 6.97  7.03 

Magnesium 24.10  24.28 

Manganese 54-57  54-99 

Mercury 198.49  200.00 

Molybdenum 95. 26  95-99 

Neodymium 139-7°  140.80 

Nickel 58.24  58.69 


TABLE    OF    ATOMIC    WEIGHTS.  365 


Nitrogen  ...........................  r3-93  14>°4 

Osmium  ...............  ............  J^>9-SS  I9°-99 

Oxygen  ...........................  15.88  16.00 

Palladium  ..........................  IO5-56  106.36 

Phosphorus  .........................  30.79  3J.O2 

Platinum  ...........................  193-41  l94-%9 

Potassium  ...................  .......  38.82  39.  1  1 

Praseodymium  ................    .....  142.50  143.60 

Rhodium  ...........................  102.23  103.01 

Rubidium..  .......................  84.78  85.43 

Ruthenium  .........................  100.91  101.68 

Samarium  ..........................  I49-I3  150.26 

Scandium  .....  ......  ..............  43-78  44-12 

Selenium  ...........................  78.42  79.02 

Silicon  .............................  28.  1  8  28.40 

Silver  ..............................  107.  1  1  107.92 

Sodium  ............................  22.88  23.05 

Strontium    .........................  86.95  87.61 

Sulphur  ............................  31.83  32.07 

Tantalum  ..........................  181.45  182.84 

Tellurium  ..........................  126.52  127.49 

Terbium  ...........................  158.80  160.00 

Thallium  .................  ...........  202.61  204.15 

Thorium  ..........................  230.87  232.63 

Thulium  ...........  ................  169.40  170.70 

Tin  .....  ,  ......      .................  118.15  119.05 

Titanium  ...........................  47-79  48.  1  5 

Tungsten  .........................  J83-43  ^4.  83 

Uranium  ...........................  237.77  239.59 

Vanadium  ........................  5°-99  5r-38 

Ytterbium  .........................  171.88  !73-i9 

Yttrium  ........  .  ...................  88.35  89.02 

Zinc.  ...  ...........................  64.91  65.41 

Zirconium  ..........................  89.  72  90.40 


INDEX   TO    AUTHORITIES. 


Agamennone X4>  25 

Allen 89 

Allen  and  Pepys 24 

AlibegofF 266,  300 

Anderson 130 

Andrews 1 18,  327 

Arago 24,  58,  72 

Arfvedson 84,  263,  282 

Aston 52,  172 

Awdejew , .  .  .  ; 132 


Bahr 137 

Bahr  and  Bunsen 356,  361 

Bailey 197,  231 

Bailey  and  L,amb. 316 

Balard 44 

Baubigny 93,  148,  180,  244,  300 

Bauer 349,  353 

Becker I 

Beringer 335 

Berlin 238,251,355 

Bernoulli 257 

Berzelius.  .  5,8,  24,  34,  38,  43,  44,  50,  58, 

72,  82,  84,91,   IOI,  IIO,  112,  121,  123, 

127,  132,  135,  146,  171,  176,  iSS,  196, 

204,  209,  211,  213,  2l6,  236,   238,  250, 

255. 263, 268, 271, 277, 282, 257, 313, 

315,  322,  325,  327,  355 

Bettendorff 349,  359,  360 

Biot  and  Arago 24,  58,  72 

Blomstrand 234,  236 

Boisbaudran 181,  360,  362 

Bongartz 226 

Bongartz  and  Classen 200,  201 

Borch,  von 256 

Boussingault 24,  58 

Brauner.  .272,  274,  340,  342,  348,  351,  359 

Breed 320 

Bucher 1 60 

Buehrig ...    339 

Buff 24,  72 

Bunsen 87,  89,  356,  361 

Bunsen  and  Jegel 336 

Burney 361 


Burton 151 

Burton  and  Vorce , .  .  .    142 


Capitaine 287 

Cavendish 24 

Chikashige 275 

Choubine 344 

Christensen 280 

Chydenius 204 

Clark 9 

Clarke 159 

Classen 200,  201,  231,  232 

Claus .  .   31  r 

Cleve. .   206,  347,  348,  351,  352,  354,  356' 
359,  360,  361,  362 

Cleve  and  Hoeglund 356 

Commaille 91 

Cooke 27,  8r,  J57,  221,  222,  224 

Cooke  and  Richards 13 

Crafts 25,  58 

Crookes 185 

Czudnowicz. 211,  346 


Davy 24 

Debray 133,  251 

Delafoutaine   205,  356,  358,  360 

De  Luca 278 

Demarcay 359 

Detnoly 191 

De  Saussure 24,  72 

Desi 262 

Deville 291 

Deville  and  Troost 235 

Dewar  and  Scott _  ,    283 

Dexter 217 

Diehl 84 

Dittmar 85 

Dittmar  and  Henderson 12,  19 

Dittmar  and  M' Arthur 333 

Dobereiner 127,  287 

Duloug  and  Berzelius 8,  24,  58,  72 

Dumas.  .  9,  39,  45,  50,  51,  72,  80,  91,  no^ 
112,  113,  119,  129,  140,  156,  176,  188, 
199,  201,  209,  213,  217,  229,  251,  256, 
269,  278,  279,  282,  289,  294 

(367) 


368 


THE    ATOMIC    WEIGHTS. 


Dumas  and  Boussingault.  . 24,  58 

Dumas  and  Stas 76 


Ebelmen 264 

Ekman  and  Pettersson 269 

Erdmanii 146 

Erdmann  and  Marchand.  ..IT,  76,  110, 
in,  166,  268,  288,  291 

Erk 347,  351 

Ewan  and  Hartog    171 


Faget 37 

Favre 147 

Fourcroy 24 

Fownes 72 

Fremy 322 

Friedel 77 


Gay-Lussac 32,  135,  146 

Genth 338 

Gerhardt 36 

Gibbs 298,  342 

Gladstone  and  Hibbard . .    152 

Ginelin 84 

Godeffroy 87,  90 

Gooch  and  Rowland   274 

Gray 98 


Hagen 84 

Halberstadt 330 

Hampe 92 

Hardin 34,  63,  74,  163,  167 

Hartog 171 

Hauer,  von 156,  271,  283 

Hebberling 184 

Hempel  and  Thiele 308 

Henry 6 

Hermann 84,  196,  206,  234,  236, 

335,  347,  351 

Heycock 88 

Hibbard 152 

Hibbs 67,  68,  215 

Hinrichs 6 

Hoeglund 356,  361 

Holzmann 345 

Hoskyns-Abrahall 171 

Howland 274 

Humboldt  and  Gay-Lussac 32 

Humpidge  and  Burney 361 

Huntington 46,  157 


Isnard 176 


Jacquelain 136,  146,  238 

Jegel 336 

Johnson 17 

Johnson  and  Allen 89 

Jolly 59 

Joly 311,  326 

Joly  and  Leidie 319 

Jones 159,  3^7,  358 

Jorgensen 313 


Keiser 15,  150,  316 

Keiser  and  Breed* 320 

Keller  and  Smith 318 

Kemp 252 

Kessler 214.  216,  218,  224,  241,  242 

Kirwan 24 

Kjerulf 336 

Klatzo 132 

Kobbe 314 

Kralovanzky 84 

Kriiss 102 

Kriiss  and  Alibegoff 266,  300 

Kriiss  and  Moraht 133 

Kriiss  and  Nilson    .    207 

Kriiss  and  Schmidt 303 


Lagerhjelm 229 

Lamb 316 

Lamy 184 

Langer 301 

Langlet 363 

Laurent  . 34,  171 

Laurie 103 

Lavoisier 24,  58,  72 

Le  Conte 25 

Leduc 20,  27,  32,  59,  78 

Lee 298 

Lefort 240 

Leidie 319 

Lenssen 156 

Lepierre 186 

Levol   102 

Liebig 44 

Liebig  and  Redtenbacher 72 

Liechti  and  Kemp ...    252 

Lougchamp ,.  .   127,  135 


INDEX   TO    AUTHORITIES. 


369 


Lorimer  and  Smith 159 

Louyet 277,  279,  280 

Lowe 231 

Lowig •    •  •     44 

M 

Maas 252 

M'Arthur 333 

Macdonnell I36 

Malaguti 255 

Mallet 84,  105,  150,  177 

Marchand 1 1 ,  72,  76,  1 10,  1 1 1, 

166,  256,  263,  268,  288,  291 

Marchand  aud  Scheerer 138 

Marignac.  .   34,  35,  36,  38,  39,  4i,  43,  44, 
45,  47,  48,  49,  60,  62,  65,  74,  no,  114, 

II.5,    Il8,    121,    122,   123,   129,  141,   148, 

196,  230,  235,  236,  284,  292,  336,  344, 

345,  35i,  359,  36o. 

Mather 176 

Maumene 34,  36,  39,  43,  75,  288 

Meineke 244 

Meyer...  , 252 

Meyer  and  Seubert i,  5,  6 

Millon 48,  167 

Millon  and  Commaille 91 

Mitscherlich 72 

Mitscherlich  and  Nitzsch 268 

Moberg 239 

Moissan 278,  279,  280 

Mond,  Langer,  and  Quincke 301 

Morabt 133 

Morley 12,  21,  27,  32 

Morse  and  Burton 151 

Morse  and  Jones 159 

Morse  and  Reiser 150 

Mosander 190,  335,  344,  351 

Mulder 6 

Mulder  and  Vlaanderen 199 

N 

Nilson 207,  354,  362 

Nilson  and  Pettersson 133 

Nitzsch 268 

Nordenfeldt 137 

Nordenskiold 360 

Norlin 287 

Noyes 16,  17 


Ostwald i,  6,  57,  71,  83,  131 

Oudemans , 6 

24 


Parker 142 

Partridge 157 

Peligot 238,  264,  265 

Pelouze 35,  51,60, 

113,  118,  188,  209,  213 

Penfield 186 

Pennington  and  Smith 258 

Penny 35,  39,  5o,  62,  64,  66,  67 

Pepys 24 

Persoz 257 

Petrenko-Kritscbenko 319 

Petterssou 133,  269 

Pfeifer 225 

Piccard 87 

Pierre 191 

Pollard  . .    252 

Popp 355 

Popper 225 

Q 

Quincke 301 

Quintus  Icilius 315 


Rammelsberg.  .  .   234,  252,  263,  337,  344 

Ramsay 149,  363 

Ramsay  and  Aston 52,  172 

Rawack 283 

Rawson 244 

Rayleigh.  .    14,  16,  25,  26,  58,  59,  98,  363 

Rayleigb  nnd  Ramsay    363 

Rayleigh  and  Sidgewick 98 

Redtenbacher 72 

Regnault 24,  25,  72 

Reich  and  Ricbter   182 

Remmler 302 

Reynolds  and  Ramsay 149 

Richards 13,  46,  82,  92,  93,  94,  96, 

97,  115,  119,  121,  123,  124,  154 

Richards  and  Parker 142 

Richards  and  Rogers 141,  152,  153 

Riche 259 

Richter  .  . . , 182 

Rimbacb 1 74 

Rivot 289 

Robinson 340 

Rogers 141,  152,  153 

Roscoe 77,  211,  257,  262 

Rose 190,  217,  234,  236 

Rothhoff 291 

Russell , 294,  295 


370 


THE    ATOMIC    WEIGHTS. 


Sacc 268 

Salvetat 1 10,  1 13,  1 18 

Scheerer 135,  136,  138,  139 

Scheibler 260 

Schiel 188 

Schmidt 203,  303 

Schneider 216,  224,  229,  232,  255, 

258,  282,  291,  292,  297 

Schrotter 209 

Schutzeuberger 301 ,  34 1 

Scott 32,  283 

Sebelien 1,7 

Sef  strom  ...* 166 

Seubert i,  322,  323,  325,  328,  333 

Seubert  and  Kobbe 314 

Seubert  and  Pollard 252 

Shaw 98 

Shinn   259 

Sidgewick 98 

Siewert ,   243 

Smith 159,  258,  318 

Smith  and  Desi 262 

Smith  and  Maas 252 

Sommaruga 297 

Spring 6 

Stas. .  6,  37,  38,  40,  41,  42,  44,  45,  47,  48, 
49,  5i,  52,  57,  61,  62,  64,  65,  66,  71, 
73,  76,  78,  80,  82,  83,  85,  128,  130,  131 

Staudenmaier 274 

Strecker 73 

Stromeyer 84,  156,  287 

Struve 81,  82,  123,  250 

Svanberg 130,  167 

Svanberg  and  Nordenfeldt 137 

Svanberg  and  Norlin 287 

Svanberg  and  Struve.    82,  250 


Terreil 177 

Thalen 361 

Thiele 308 

Thomsen. .  13,  22,  30,  57,  69,  71,  83,  131 

Thomson 24,  58 

Thorpe 192 

Thorpe  and  Laurie 103 


Thorpe  and  Young ...    1 89 

Tissier 176 

Torrey 151,   180,289 

Troost 84,  235 

Turner..   38,  64,  121,  122,  123,  128,  166, 

167,  282 


Unger 221 


Van  der  Plaats.  .  .  6,  57,  71,  77,  83,  131, 
149,  200,  210 

Van  Geuns . .       5 

Vanni 98 

Vauquelin 24 

Vlaanderen 199 

Vogel 6 

Vorce 142 

W 

Wackeuroder. ... 287 

Waddell 258 

Wallace 44,  213 

Warrington 33 

Weber 217 

Weeren 132,  285 

Weibull 196 

Wells  and  Penfield 186 

Welsbach 353 

Wertheim 265 

Werther 184 

Weselsky 298  * 

Wildenstein   241 

Wills 271 

Wing 338 

Winkler.  .  . .  182,  195,  297,  305,  306,  307 

Wolf. 337,  340 

Woskresensky 72 

Wrede 24,  72 


Young 


189 


Zettuow 260 

Zimmermann 266,  300 

Zschiesche 347,  351 


DATE    DUE   SLIP 

UNIVERSITY  OF  CALIFORNIA  MEDICAL  SCHOOL  LIBRARY 

THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


2m-ll,"29 


